My first T5 installation was in my 1965 C10. I had my original DS cut shorter by a DS shop and then the S10 slip yoke was put on with a conversion U-joint. Worked great. It was pretty expensive though.
I used a worksheet supplied online by Denny’s Driveshafts. (Just Google that name).

If I recall, I used worksheet B to get the dimensions for the DS shop to work with. The guy at the shop looked at the sheet and gave me a thumbs up. It was all he needed. Worked out great.

Years later I installed a T5 in my 1963 C10. I had read somewhere that an Astro van DS was the correct length, so I searched through my local salvage yard. Unfortunately, the salvage yard I frequent uses a large forklift to set the vehicles and damages 90% of the driveshafts.

I stumbled upon a DS just laying on the ground that was the correct length. I had no idea what vehicle it came from but it had the correct slip yoke (with a balancer). I bought a new conversion U-joint for the rear of the DS and it bolted right up. That 63 drives like a new truck and I saved a lot of $$$.

Here are pics. Research shows me the DS came from a Chevy Blazer. Not all Blazers will have the correct DS, so the sticker ID is important to match mine. I recently grabbed another DS just like it.
Attachments
B9F8C914-9B28-485D-BB0A-5C32D3CB8809.jpeg (257.11 KB, 103 downloads)
60106600-8BE4-4A88-A7DD-AC4A3CAAE14C.jpeg (383.82 KB, 103 downloads)
F6AE8817-6FEB-4223-84A7-AF7D9A8F8FAE.jpeg (168.99 KB, 103 downloads)
A6AA376B-09C5-4F95-8BA8-7B97FD51CF7A.jpeg (336.19 KB, 103 downloads)
230F2920-7F30-4204-9DE0-D348B606F9A1.jpeg (110.82 KB, 103 downloads)