Splicing in the subframe from the 2nd gen F-body (Firebird/Camaro) is quite popular. Good brakes, strong suspension parts, lots of options for engine/transmission combinations. Relatively inexpensive and still plentiful.
There are "kits" for such things, too. A good street rod website or magazine can clue you onto the "who and where" details. Generally higher costs.
Registering street rods varies from state to state, regarding VINs and what "year" the vehicle actually is. Check with local officials.