Not special plugs... It came with heads like these:
No real performance or milaege difference, just a different look. Tune her up properly and don't expect technology to beat physics. It takes a lot of power to move a 2 ton shoe box.
I have heard of trucks with modern engines and 4 or 5 speed modern transmissions getting very high teens reliably, but that's so much money that you should look at the improved milage as a side benefit because you'll never recoup that cost in saved gas.
