tough transfer case question for tech guys

Right now I have a stock 231 or 241? transfer, cant reat the numbers well. The question I have is quite long so bare with me.
I have an 88 chevy 1500 4x4 auto with a 700R4 tranny.
It will be used to haul a mud truck and was told a th400 was my best option.
I bought a th400 w/np208 still hooked to it. I only got the 208 because of the bigger input shaft.
The advice I got was take the input shaft out of the 208 and swap it with the 231/241. If anyone out here has ever done it can you tell me if its interchangable? I'd like to know if it is before I drop since this is my daily driver. I'm getting conflicting reports from different tranny shops.
Any help on this would be greatly appreciated. I need to haul my mud truck this weekend to the runs.

Thanks,Don

Don, your hauling a mud truck with a 1500? What is the towing capacity of the half ton?

Don, your hauling a mud truck with a 1500? What is the towing capacity of the half ton?
I know its a big no no but its way cheaper to do it this way than to buy a new truck. I've been going for years now and about 75% of the guys there are hauling with a half ton and just take it slow. I'm never hauling more than 20 miles. Its something my wife and I started doing just for fun

Don