If turning the wheels is affecting the idle thats a symptom of a loose belt... that would probably have nothing to do w/ the carb. Look for a loose pulley / tensioner and see if you can get it tighter. When it comes to putting a crate engine in it really depends if you are going to do / able to do the work yourself. If you end up at the shop it could cost anywhere upwards of $2,500 installed. It's really not complicated to do but the whole 'taking the car to the shop' game is a whole different ballgame that requires estimates planning and research b/c you could come up with a wide variety of answers on what this will / should cost lol