i installed the engine with LT's on. its really not that bad. just tough to put the tranny in. but i did it. if i were you i would try to intall it with the tranny on first. and if it doesnt go than unbolt it and then stick it in after.
but it was pretty hard to put the tranny on. but it is possible. just have to be really careful you dont bust up the clutch.
the motor fell right in, the LT's didnt get in the way!
good luck