Re: motor clearance for new seating
the motor doesnt need a ton of space, just enough so it has an inch or so around it on all sides is plenty(to account for slight vibrations and stuff)
how much you need to work around it is really up to you

Make sure to give yourself enough space to remove the manifolds and risers(so you dont need to pull the engine if the engine needs new ones), and make sure you can access the oil filter, and fuel filter, and change the belts.