Is there such a thing and if there is, why or why should they not be used? There is a bolt I have a bitch of a time getting to to tighten (the rear one on the passenger side)

I don't know about torx. Your probably thinking about 12 point. A 12 point socket is thinner. Also take a close look and see if they have a groove cut in them for use with keepers. These will lock them on so they don't back out.

Ive never heard of torx bolts, but you can get header bolts that use an allen wrench to tighten them.

I found allen/hex locking bolts in Jegs. $32 for SBC. Not too bad for quality and ease of installation.