I have only seen a real Sprint Firebird once, many moons go. A guy was trying to get exhaust head pipes for it at an AutoZone. No luck. Here are the 4 barrel intake and split header exhaust manifolds. SPRINT manifolds

I know it takes a Quadrajet, but the right one would be pretty hard to find. The SPRINT cam I believe is available. In Smoke Signals I see there is an OHC chapter. I'm sure they could provide parts or point one in the right direction. I actually miss my OHC engine. It made a lot of power for a 250. The light weight let the Firebird handle like a champ.