Since you said you don't mind drilling some holes....
My '65 C10 had a 1990 Chevy truck bench seat in it when I bought it. Nice comfortable seat, back folded forward, and it had a flip down center arm rest. That series of truck was made from 1988-2002.
So if your not to concerned about originality... there's a bunch of seats that will work great for you.
_____
John
