I just purchased a running 70' 472ci with the th400 behind it for the pricey sum of 200 big ones. I have a 74' k5 with 350/th350 and np205. I planned on trying to unload the entire drivetrain. My question is which would be the better way to go. Find a th400 with a np205 and buy the adapter plate to mount it to the block or use the th400 that came with the block and buy the tailshaft and adapter for a 205. I want to know if there are any advantages to either.  

Caddy has a unique bolt pattern on bell housing so you need to adapt its tranny to Tcase. Also Caddy came with a THM475 which is a beefed up  THM400.  

So basically it boils down to me buying one adapter or the other. No real advantage either way. If anyone knows where I can find either the bellhouse adapter or the tailshaft adapter the info would be greatly appreciated.  I was very happy with the setup i have until this big block almost fell into my lap. It was very hard to pass up 375hp/535fp.  

Yes there is a advantage, the caddy THM475 is a heavier duty version than your normal THM400 you find in a bone yard. There was 4 versions of the 400, a 375, 400, 425 and 475. 4x4's that had them usually had a 375 or sometimes a 400 but never a 425 or 475. Motor home chassis used 475's too. I would use tranny that came with engine for sure or one just like it (another 475)  

early caddi bells are different, later models share the BOP bell.

the th375 is a 2wd only, 27 spline longshaft (same as the th350) found in the large 72-76 chev's, caddi's and BOP's...it uses the same internals as the 400 with the exception of the size of the output and have taller pistons which use less clutches than the 400.

the th400 from (63)64'-92, is a 32 spline output used in trucks, 4x4's, some caddi,s chevy, and the BOP's... the most common and widely used.

the th425 is a frontwheel drive transaxle tranny. 66'-79' in the big o'l tornonado's and large fwd caddi's

the 475... never found in a caddi, came out in 71', is a 32 spline output/bolt on yolk, (some have straight cut planetaries that offer a lower 1st and 2nd gear ratio). used in heavy trucks, vans, busses, and motor homes.

they all share most parts with the excecption of the th475's planetaries. and the th425's case.  

Your are wrong on the 475 in caddies. It was behind 472 and 500. And yes you can beef up a 400 but why bother when you have one already? Also there was two 375's. There was a 375 based on THM400 and a 375B based on THM350.  

LMAO......  

Thanx for the input guys.  I called trandap and got a price on the bellhousing adapter which is $140 and the tailshaft adapter which is $600. Not to mention I would need to have my 205 machined to accept the the larger input bearing. Needless to say,  I am going to go with the th400 4wd trans and bolt a 205 that has the correct input already. As luck would have it my buddy just bought a 1ton pickup and is going to trade me his tranny and transfer for my caddy transmission.