[Myron Piatek]

Without actually checking, I wouldn't think a 1/2 Duster/ 1/2 Demon would be allowed. But '73 and '74 Duster front clip parts are the same. Not too hard to find.

318 4 barrel doesn't exist in any NHRA or IHRA Stock combos for '73 or '74.
318 2 barrel of either year, 340-4 for '73 or 360-4 for '74. Other options include IHRA-only crate motors that are or were available over the parts counter and accepted by IHRA or Stock GT which could use a later model year 318-4.

You need to get some rulebooks and do lots of research!