T5 swap & driveshaft length?

[67 twins]

I picked up a T5 from an S10 that I plan on putting on my 67 C10 v8 truck that has a 3 speed in it now. Looking at what I need to make this work it looks like the T5 is about 3 3/16 in. Longer than the 3 speed (best as i can measure with the Tranny still in the truck)meaning I need a equivalently shorter driveshaft. After talking to the driveshaft shop & being quoted $350 to shorten my shaft, I started thinking.
The six cylinder trucks mount the engine & transmission further back in the chassis so a six cylinder 3 speed truck should have a shorter shaft. Well after measuring what I could it looks like the transmission crossmember in the 6 cylinder trucks sit somewhere between 3.4 & 3.7in. Further back.
I'm thinking this is close enough that a driveshaft from a 6 cylinder 3 speed truck might be just what I need. Anyone tried this before or would anyone like to comment?