The 305 is built with factory cast alloy pistons. Although it's not their
intended environment, the pistons will endure a signifigant amount of
performance abuse without protest. The most important thing to
check for is adequate valve-to-piston clearance. Unleaded premium
works well in this combination, but be careful not to rattle the motor
too much with poor quality fuel. After truing the deck surfaces, we
had seven pistons .014-inch down in the hole and one just a tad
further. With the stock 305 head gasket, this gives a piston-to-head
clearance of .035-inch. Just right. The exhaust valves were a little
shy on piston-to-valve clearance, so they taped off the cylinder
crevice and dressed the valve pocket in the piston with a high-speed
sanding disc.