1983 C10 305 to 454 Swap

[Wojo21212]

I am in the process of installing a 454 & TH400 out of a 1979 C2500 LWB GMC truck into my 1983 C10 SWB that had a 305 with a TH350 (Motor & Trans were gone when I bought the truck). After installing the motor & transmission the transmission crossmember doesn't line up. I do know the TH400 is 2 3/4" longer than the TH350's (I think). The original transmission mount is like 7"-8" too far forward. Is this normal? I am going to buy an aftermarket transmission crossmember for dual exhaust & mount it to the frame. Also what is the best long tube headers for this set up that has good frame clearance & won't burn up any spark plug boots? I am running aluminum heads on this motor. Thanks!

 

[Mr Clean]

 

[bucket]

Howdy from Ohio!

There's a lot of variables here and there's also several ways to skin that cat.

But in short... the original th350 should have been a long tail. Your th400 from your donor truck should be a short tail with a bolt-on yoke (shorter overall length than the long th350). If so, you can remove the bolt-on yoke and get a slip yoke from an 80's K10 truck, Suburban or K5. Using the K10 slip yoke, the original driveshaft will be close enough in length to work.

There should be a second set of holes in the frame to use your original crossmember.

Headers meant for a '68+ Nova fit well.

 

[ali_c20]

Welcome from Austria. Pics please.

 

[legopnuematic]

Welcome from Missouri.

 

[WFO]

Welcome from the Texas Panhandle.

 

[Catbox]

Second the Nova headers.
I got these from a buddy as he had new ones for his Nova.
They bolted right up and fit great.

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We have a manual transmission and they clear everything with out any issues.

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Looking under the truck the Nova headers tuck up real nice like...

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Putting my head and phone on the ground, you can then see the collector and that they are higher up than the front crossmember...

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[dabranco12]

Second on the slip yoke, also I have a spare slip yokes 1 bolt on 1 slip style, and an extra universal cross member for dua vs l exhaust on a 2wd. I am in the same process as well just on an 84 suburban. Overall driveshaft length is different due to transmissions being different. You also need to set up a system to operate the passing gear for the th400. My next question is how is the 454 built? Also hooker 2454hkr headers if you going new

 

[bucket]

Second on the slip yoke, also I have a spare slip yokes 1 bolt on 1 slip style, and an extra universal cross member for dua vs l exhaust on a 2wd. I am in the same process as well just on an 84 suburban. Overall driveshaft length is different due to transmissions being different. You also need to set up a system to operate the passing gear for the th400. My next question is how is the 454 built? Also hooker 2454hkr headers if you going new

That's why I mentioned the slip yoke from a K10. It is 32 spline, but longer than the typical 2wd yoke. When going from a long tail th350 to a short tail th400 that originally had a bolt-on yoke, the K10 yoke makes the shaft long enough to work ok. It could stand to be 1/4-1/2" shorter, but it works fine.