Coming from a guy who has machine shop background...
The #48 heads will NOT give you anything at all. I have flowed these heads in stock form. +/- a few percentages...the 16 and 48 heads flow the same. SAVE YOUR MONEY!
The difference is in the exhaust manifolds, cam, carb and to a lesser extent, the spring setup. You can replicate the same performance as a RAIII #48 motor simply with a cam swap, better ehaust and proper tuning.
Simply put...the RAIII motor ratings were due to cam, carb and exhaust differences over a typical 400. Yes, some RAIII had open ram Air scoops. That moniker was not really a huge difference over closed scoops. If you are going to replicate the RAIII, keep the heads and buy some aftermarket longbranch manifolds, RAIII regrind and tune.
However...you've opened up another can of worms...Need to know all of the engine, trans rear gearing particulars and budget.
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
