I have a 1973 Chevy blazer that came stock with a 350 and an NP203 transfer case, as it is a full time four wheel drive.  I'm wondering about the compatability of swapping the 350 engine and th350 tranny for a 454 and th400.   My question is if the th400 will match up with the np203 or if modifications will need to be made.  Also if it will handle the extra power of the 454.  If anybody knows about this I would appreciate the comments.  Thanks  

I don't know about the t-case since I'm new to the offroad world, but I know that a Turbo 400 should be able to handle something like 800 ft lbs or more. So not only can it handle a 454 motor, it can handle motors like a blown 502 or a naturally aspirated 572, 640 etc. Just make sure it's in good condition first, maybe rebuild one. 

Thanks for the reply.  I know the 400 can handle the power of most engines, especially if it is built properly.  My main concern is how the np203 transfer ccase will mount with the th400.  I don't know if this has been done since the 1973, to my knowledge, didn't come with anything bigger than a 350 ci engine from the factory.  If anybody else has a fulltime four wheel drive that has a 400 ci engine or better and might know a little about this please let me know. Thanks   

Honestly the TH350 will handle the power of the 454. And it will bolt right up. The only thing I would change the tranny for is if it is slipping now, or massive amounts of mileage. Other than that the TH350 loses less horsepower through it then the TH400 does. As for the transfer case I think you would be better off with a NP205 or NP208 commonly found on early 80's Suburbans already hooked to a TH400.  

Save the money of not replacing the transmission and do what he said, put it into a NP205...damn good t-case, gear driven too.  That TH350 will be fine.  Plus you can ditch that full-time ####.  

Yes it will bolt right up!! IS it a long tail shaft or short tail shaft 400? Id stick with the 350 though and use the stronger transfer case.  

I have a Small block 400 bolted to a TH400 and a NP203 on the tail end. It came from the factory like this so i "believe" it should be possible. I have no problems even though i ave about 385 HP and 430 lb ft.

Ok you have a complete ready to install unit . Pull the old drop in the new. It will be a direct drop in. The 400 is an upgrade over the 350 the tail shaft length will not matter now since you have a married pair.( id replace that drive shaft seal with a new one) Good Luck!!!!