R1 Option: 289 CID, 10.5-1 compression, 4 Barrel AFB, hotter cam than standard. Estimated HP 240

R2 Option: 289 CID, 9-1 compression, Dual belt driven Paxton supercharger (6 in. crank pulley / 4 in. blower pulley), 2.75in. pressure hose from blower outlet to cast aircap on top of pressure sealed AFB carburator. Estimated HP 290

R3 Option: Special production order from Paxton (Granatelli brothers). 304.5 CID, 9.5-1 compression, Dual belt driven Paxton supercharger (8 in. crank pulley, 4 in. blower pulley), special cam, heads, pistons, tube connecting rods, cast exhaust headers, non-sealed AFB carb in a large cast pressure box. This car also had solid inner suspension bushings for tighter handling. Only 9 were sold as production orders, however there are cars in which these engines were installed afterwards by owners, etc. There was an interesting option offered with these, called a Carb-u-meter, which was installed in the dash console. This included a vacuum guage and 2 carburator adjustment screws to fine tune the engine while driving.

R4 Option: 304.5 CID, 11-1 compression, dual 4 barrel AFB carbs, Non-supercharged, Only 1 production engine installed and it was in a 64 Daytona.

R5 (?) Andy Granatelli created a dual Paxton supercharged, intercooled, fuel injected engine with a 304.5 CID, called it the "Duo Cento" to signify '200'(mph?). It was installed in an avanti to run in speed trials at Bonneville. The fuel injection was a modified version of the Bendix injection system used on aircraft of that era and claimed an output of over 500HP. In speed runs, the car exceeded 195 mph. After the tests, the car was sidelined and the engine removed to storage where it was disassembled many years later. None of the original parts are known to exist .