i don't remember the size but i got some bolts at the hardware store for like 35 cents each... 1 inch long, 7/8 threads maybe?
unless you need the threaded insert, which you dont on the back of the head, i wouldnt pay 10 bucks for the TFS plugs.
I think you would lose a lot of midrange torque by going to 3 in. exhaust.
1 3/4 primaries and 3 in. pipes are designed more for 351 applications.
my .02