"Some" money sure. I had a 390 in a 67 GT fastback that was worth "some" too
Did you see what bnickel posted? They made 170,000 Mach1s, no matter what engine code you had it was just not that rare, which leaves the 428 as the top dog and all the others as worth less. The 428cj is about the most valuable non-boss engine you can have, the 65-67 K-code being a very close second and debatably in 1st place (but obviously not for a 69 car LOL).
I say restomod, but don't do irreversable things if the car is rare. I welded in a rollbar and subs on mine, but it is a 67 C-code and they made TONS of those, MANY more than all the Mach1s combined. Even the convertible factor on my car doesn't make it even semi-rare, they were everywhere back in those days.