A 6.1 long block has all the mounting holes and such that you need, same oil filter location and any adapters that may come on it are an easy swap to use your 7.7 adapters. The oil pan and sucker tube need swapped on (not hard) timing cover needs swapped (not hard), intake bolts on and it's much easier to swap the engine when you have the intake off any how. Ex manifolds are different but easily swap and you probably want to put in new bolts anyhow... the computer will notice it running leaner and add fuel for you, not perfect but will get it close (a tune will certainly help just like it would on a 5.7 but is not absolutely needed, my ram 1500 with a 6.4 runs awesome with a stock tune and that is an even bigger difference). If you were to buy a 6.1 long block from say auto zone it would litteraly bolt in exactly like a 5.7 long block from auto zone. No need for this to be complicated.