Right now prices on SC are pretty reasonable and the 3 liter engines were some what indestructible, same can also go for 3.2. Most SC that are in good shape, are still selling in the low to mid teens. I don't think that it would be a problem going back to 3.2 heads, but if the 74 is running okay why would you want to take on that type of expense, unless you are doing the work yourself. If the 74 has been updated with a 3.2 and weber carbs, it should be getting over 200bhp already.