I'm looking into swapping in a Saginaw four speed from a car (not the truck granny low four speed) into my '66 C10 that has a 250 and three speed on the column. I'm wanting to keep it column shift and add separate cable under the dash for the reverse lever.

What is involved with swapping from a three speed to the four speed? From pics it looks like the four speed has a longer tail shaft, I'm guessing I'll have to shorten the drive shaft? Can the four speed hang from the stock bellhousing or will it need it's own rear crossmember for support? I believe I'll have to lengthen/modify the shift rods, I can weld so that shouldn't be a problem. Anything else to look out for?

The three ring Saginaw ratios from lower powered cars have 3.50, 2.47, 1.65, 1.00 gears compared to the 3 speed's 2.94, 1.68, 1.00. My plan is to swap to 3.08 gears and the overall ratio in first would be the same while dropping about 600 rpm at 75 mph. It has a stock 250 for now but I plan to eventually rebuild the head, add lump ports, an Aussiespeed intake, header, and possibly Holley Sniper and a small turbo.

I swapped from a PG to a Sag. 3 speed then to a 4speed, I would have thought the 3speed would have had a Trans tail mount. Unless it was the stubby 3speed. But Yes if should have a tail shaft mount.

It probably could hang out there but it is so easy to build or buy a crossmember/mount I'd do it. It will make it stronger. You'll have to modify the shift linkage and shorten the driveshaft if you aren't lucky to find one like I did when I put a Saginaw 4 speed in my '53 pickup. It will bolt up in front.

Thanks for the replies and suggestions! It does have the short tailhousing without a rear crossmember, it's only hung from the bellhousing with a crossmember under the bellhousing. After doing more research it looks like a Super T10 also could've had a higher number first gear- 3.42 on the six groove version, and an ST10 should hold up to boost better later on.

With the Super T10 The higher the number the smaller the Input shaft is so the weaker it becomes. so a 3.42 is s smaller Dia. then that of a 2.88 or 2.42 first gear. So if your not racing it, that 3.42 will be a nice first gear for you. My tranny guy told Me that because I race my L6. He said Yeah it would be great to run the 3.42 It will leave the line like a rocket But only one time IF THAT. lol He knew all the things My Twisted6 has broken so he said either nothing lower then a 2.88 Or buy a High end Tranny.

I ended up finding a two ring Saginaw with a 3.11 first gear for $100 locally. It seems like the newer three speeds in 71-72(?) C10s had the longer tail shaft that would match the length of the four speed Saginaw, so I should be able to find a used driveshaft from one of those trucks pretty easily. I'll update the thread with pics once I start the swap.