Does your existing truck have a 420 in it now? You might come across a 465 which would also work. You can also probably get a higher diff. ratio for the 14 bolt, full flotation, I presume. However, one needs to match up front/rear bolt patterns, are you going to use front and rear axles from donor?
Ed
See if I can throw this out in a concise way.
Parent truck: 1951 wheat truck. 6400 I believe. I have taken the engine and drivetrain out, but these were the contents- 235 I6, SM420 transmission, original banjo rear end with 6.13 gears
Answer to your question- Yes I have a 420 now. I would like to use it for the reasons that I have it, and I'm not interested in the SM465 ratios as I plan to use this truck for real work like hauling grain or dirt. I like that super low 7.05 first gear to pull out of a field onto a road under load.
Donor vehicle: 1991 P30032 chassis RV. As it sits it has- TBI 454, 4L80E, 14bolt with 4.56 gears
Would like to make the parent 1951 truck have the combination of TBI 454, SM420, 14bolt with 4.56 gears.
4.56 gears will move me down the road at a comfortable RPM. The 454 will have the a$$ to push it. The SM420 has a wide set of ratios that the power of the 454 can cover. The 14bolt rear end has disc brakes. I'll rob all the modern brake components i.e. booster/master cylinder. I'm still figuring how to make the front disc, but that's a different thread.
