5/16 wrenching header bolts

Early 80's smallblock's used a long hex nut manifold nut. I turned those down on a lathe, leaving the hex on the end, past the tube. They worked great in conjunction with studs on the end locations. The other tight locations, I used allen socket screws, and cut an allen wrench tip off, insert then use an open end wrench or the shortened allen wrench with a small tube for leverage.
Leigh