Well, I can answer a couple of your questions...
No, you cannot use a stock bore 102mm head gasket. Yes, you can use a 105.5mm head gasket. That is what cometic gaskets always sends me
for my 105mm builds. I run studs on my 108mm build, but can't remember who I got them through, sorry.
One other thing you might consider doing is o-ringing the cylinder. I'm sure many shops do it, but I've always had great luck with Sredrum's Race Carbs in
Ohio doing mine. Runs ya about $80 shipped if I remember correctly. He is a sponsor on yfztech if you were interested in contacting him.
Hope that helps- Kris