I've decided to ditch the Saginaw tranny and go forward with a T5 for my '47. I have an 8.5" with 3.42's and am going to use 235/75-15 tires (29"). The engine is either going to be a stock 250 inline 6 or a mildly modified 250 with flat tops, a small cam, headers, and 4 bbl intake & carb. The one that I have needs a rebuild, and if I go with that one, it will get the above mods. I'm trying, though, to convince a good friend out of the bone stock one that runs perfect from his '72 Nova. He already told me I can have it when he puts a smallblock in it, but he's a bit of a procrastinator for his own stuff since he has two shops that he runs (plus has 2 drag cars).
Anyway, I've read tons about the swap and have printed off lots of info with tag numbers and so forth. My question is this: is there any T5 that can bolt to a GM bellhhousing (which I already have from a 250) without an adapter plate? I'd like to just bolt on and be good, but am still unsure which one I can do that with and which one needs modified or needs an adapter. I will be using a new stock flywheel for a 250 and a stock bellhousing for a 250. I've gotten some parts recently from a local (large) salvage yard, and they have a bunch (15-20) T5's on the shelves for sale (around $250-275?) from various S10s. I've done the RPM calculator many times, and I'm thinking that any of the ratios would work with the 3.42's. I just wanted to have the process of bolting up to be as easy and simple as possible. Any thoughts are appreciated.
Thank you.
Wayne
BTW, I saw Lugnutz recent (and very imformative) post about this subject, so if there are multiple T5's to choose from, which would be the best (most economic) one to start with?
A few build pics:
Truck picsWayne S,
I believe I have your answer. I have gone through the same decision making with my own truck.
My truck has a 250 from a '71 C10 and it's all stock. I'll be using a 1965 C10 3.73 rear diff. I have considered using a 3.42 rear that's leftover from my 1966 C10 parts truck, so I have done the calculations for that one as well.
I will be using my factory 1965 cast iron bell and clutch linkage too.
Please allow me to be so bold as to tell you what to do rather than simply list your options. I'll try to convince you I know what I'm talking about later. LOL! 
Your 250ci and 29" tires will work best with a 0.86 OD gear if you keep the 3.42 rear. Plain and simple. That means you need a 1993 or earlier T5 from an S10 or S15 truck and it should have a 0.86 OD gear (I do NOT trust the charts that list TAG#s and gearing and I can prove that many are wrong - so beware of this and check the T5 gearing before you buy). Neither the Camaro or Astro vans have the 0.86 OD gear.
If you have a 3.73 rear and 29" tires then you can use a 0.72 OD gear but not anything taller like the 0.63 in the V8 Camaro T5.
I say this because my forum friend Ryan has a '67-'72 model C10 and a 3.42 rear with his 250ci and he says that his 0.72 5th gear will bog the engine on hills (usually).
First, I'm going to assume that you will not be driving your truck over 70MPH that much. That's just my assumption so I could be wrong.
Calculations show that a 29" tire and a 3.42 rear with a 0.72 OD will have the engine doing only 1854 RPMs at 65 MPH. That's not too bad but if traffic or a hill slows you down to 55 MPH then you will only have 1569 RPMs and will need to downshift. So you will only have a sweet spot for OD from 60-70 MPH.
I think OD should allow you to use the truck at highway speeds from 55 thru 70 without downshifting. A 0.86 OD gear with a 3.42 is right in the sweet spot for a 29" tire. That combo gives 1874 RPMs at 55 MPH, 2045 RPMs at 60 MPH, 2215 at 65 MPH, and 2385 at 70 MPH.
Here's a list of what will bolt up to your bell without any modification.
Astro van or Safari van T5 (all of them are non-WC) will bolt right up. Astro/Safari T5s come with a 4.03 or a 3.50 first gear and a 0.72 or 0.73 OD gear.
The V8 Camaro or V8 Firebird T5 from 1982 thru 1992 will bolt right up as well because the IS is the correct length. If you want to keep your bench seat then you will need to remove the Camaro tail housing and do the S10 tail housing modification. You can see how I did mine
on my website. One other problem here is that many of the V8 Camaro T5s have a 0.63 OD gear which will definitely bog unless you have enough torque at low RPMs to carry it. A good thing about the Camaro T5 is that just about every V8 Camaro T5 from 1982 thru 1992 has a cable speedo drive. If you ditch the bench seat and bring the shifter up through the truck floor in the Camaro position then no modification would be needed and you could keep the cable drive speedometer.
I
CANNOT confirm what I am about to say next. I have a V6 Camaro T5 and the splines on the input shaft seem to be cut along most of the length of the input shaft. Simply cutting off about 3/4" from the end should (I want to emphasize
SHOULD) allow it to bolt right up without an adapter plate. So theoretically, a V6 Camaro T5 might only need a bit nipped off the IS and then no adapter plate. It will also need the S10 tail housing swap if you use a bench seat.
In summary, I think you would like the drivability of a 0.86 OD gear with a 3.42 rear and 29" tire. There are ways to get around the $160 adapter plate but I have no personal experience. The toughest thing about using an S10 T5 is finding one with a cable speedo output. If you have upgraded to a newer electrical impulse style gauge, then shopping for and finding a decent T5 should be fairly easy and more economical.
I have a passion for the T5. Please feel free to PM me and I will be happy to help if I can.
