So my buddy dropped off the 454 and turbo 400(2800 stall) today!Going to start the transplant on the weekend.My questions are:If for the sake of being lazy I want to keep my turbo 350 tranny will the new stall convertor from the 400 move over to the 350?Has any one had experiance running a turbo 350 behind a mild 454?Any problems?If I decide to put the turbo 400 in what length does the driveshaft have to be?I believe the engine and tranny are out of a 1974 chev 3/4 ton block casting #361959.The tail shaft on the TH 400 is 4 ". So I don't know if that is a truck tranny or out of a car.Thanks for all the help,just want to make sure I understand everything before I begin.

I don't about the drive shaft length, but I believe the touque converter bolt patterns are different between the two. If memory serves me right, the TH350 is 10.5 and the 400 is 11.5. All you have to is get a dual pattern flex plate like this one.http://store.summitracing.com/egnsearch.asp?N=700+400304+302395+4294840133+115+4 294925073&autoview=sku

Hey thanks for the reply .So by buying that dual hole flex plate the convertor will work?Only the flex plate is different?

Thats it. The TH350 will bolt right up. I just did the same thing. I left my tranny in place and just dropped in the 454. Peace of cake. Double check the bolt pattern before you order another though. I had originally wanted to run the 454/400 combo, but changed my mind when I realized I had to cut the drive shaft. So, I had already ordered the stall for the 400. I just had to swap out the flex plate and that was it. The 350 will be a little weaker than the 400, just dont overdo it. Mine setup is just a cruiser and sees no track time, so the weaker 350 was no problem.

I ran a th350 for 5.5 yrs behind my high 11,low 12 second 454 with no problems. After the 505 was installed the th350 couldnt handle the pressure, it even took alot of work to get a th400 to hold up. The driveshaft measurement is something you would have to do after the install. The converter will work on either transmission and most aftermarket flexplates are dual drilled.

So just out of curiousity will I have to change the oil pan?One guy that I was talking to from a local speed shop seemed to think that the 454 Chevelle had a different oil pan then that of the truck 454.The oil pan doesn't look really deep but I have never seen a Chevelle BB oil pan before so I don't know.

The oil pans are differant. You need a Chevelle pan for sure. :D

by the way the 400 yoke is different than the 350, driveshaft length is same though. i run a built 350 behind my big block 500+ horses with no problems.fyi i work at a driveshaft shop.

The 400 tranny I have still has the yoke on it.I heard that th TH350's yoke is designed to have some in and out movement where as the 400 yoke is solid.Does this mean I have to have a split driveshaft(steady bearing) on the new driveshft?I could be mis-informed,it wouldn't be the first time!So if the drivshaft length is the same can I just re-use my current driveshaft and just put on the 400's yoke?