Everything you can do to make a short block and valvetrain easier to roll over is going to pay dividends in fuel economy. It's a huge part of the magic used to get those amazing power/economy numbers from modern engines like the LS series.
Quick crude example...
Take two mostly identical engines, except one shortblock requires 40ft/lbs to roll over using regular oldschool piston rings, the other uses a modern low-tension ring pack and requires only 13ft/lbs to roll over. That's a constant savings of almost 8hp at 1500rpm. If your car cruises at 2500, that equals a constant savings of roughly 13hp while you are driving down the hiway.
As a bonus, WOT at 7000rpm, the low-tension shortblock would have about 36 more hp on tap.
If you decide to go old school, do yourself a favor and build it with modern hyper pistons, skinny low tension rings, and a compatible cyl wall finish using torque plates. Not only will the engine will last a lot longer, but even more important, less friction in the cylinders will pay fuel economy dividends for the entire life of the engine. Less friction in the cylinders also means less heat being put into the cooling system. Oil temps come down as well. Proper clearances and thin synthetic oil will help too.