unless you are saving the pieces you cut out,to put back in some day,,the templets that they will give you,,if they still provide them, there cut out is usually way bigger then you really need,, if you dont care about saving the piece,, do it by trial fitting,,you will also need the engine in,to try fitment as you go,,,
if you remove the engine ,,, and cut it open,, and put it all back in only to find out you need to remove more or you removed too much,,,
as stated,, car up in the air,, front tires off, make it easier to deal with,,,