i have a 170 slant in my valiant, and the exhaust manifold is cracked. i cleaned up a manifold, planning to swap them, but i realized the new manifold has a less than functional stove flapper mechanism. i have a spare 225 that was running well when pulled about a year ago. I was planning on possibly rebuilding it and swapping it in, but could I just swap the manifolds and carb in the meantime? would I have to change the carb adjustment to make this work well? Carbs are not my expertise and I would rather not futz with them as much as possible

Yes, the manifolds and carb will just bolt to your engine, but you will have to pay attention to the smaller details such as the throttle cable linkage and adjustment ad the kickdown linkage and adjustment (if your vehicle has an automatic transmission). You will most likely have to "futz" with the carb a bit, I am afraid. If it has sat for a year I would at least flush it out with some carb cleaner.

Carburetor operation and repair manuals are available HERE.

the linkage adjustment is something I can deal with, im not too concerned there. i also will give it a good clear out with carb cleaner. im more worried about having to change jets and so on.

The 225 carb may or may not be jetted to rich for your 170. Only way to tell is to put it on there and try.

A 225 carb on the 170 is considered a "performance upgrade". If it is a Carter BBS there are no jets available. If a Holley, then the jets for the 4v will work and are available from most auto parts store.