I have an 05 Buick Rainier with the 5.3l motor. I believe that it is the LM4. Can I interchange that motor with any of the other 5.3s? If so, what years? Would I probably have to put some of my old motor accessories on it?

 

This should interchange. The LS4 front-drive is the problematic engine with the different bolt pattern. Make sure you match up your crank reluctor; I think this will be a 24x and so you'll want to stick with gen III (05-earlier) engines. 6.0s from those years are externally the same size and bolt pattern(just larger bore) so if you find a deal on one those it's worth the thought...basically bolts in.

 

Also the LS4 has a shorter crank length then all other LS's. This is to accommodate the front wheel drive.