When I was building mine I had to put in and take out the engine a couple of times to get it right. I used a type 4 seal, as stated above, and figured everything so there would be a 3/4" to 1/2" gap between the engine tin and the stuff I was making.
I took a few pictures but, everything is black and its hard to see any detail....If you want they are in Jeromes Streetbeast.
BTW: Be sure to wear a good pair of gloves when working with sheet metal...I gashed my hand pretty good....enough to freak out my wife.
Later,
Jerome