A paddle-wheel water pump will cavitate- generate bubbles- and stop pumping much water at some engine speed; street engines usually do so around 5000 rpm. Changing pulley ratios is common; smaller ones lead to 'overdrive'- pumping more at low engine speeds and not pumping enough (due to cavitation) at higher engine speeds. The old trick of clipping every other impeller blade off a stock pump moves cavitation to higher engine speeds, as does a larger pulley (underdrive). I've made a few pump pullies in several ratios for street machines that worked for their owner's purposes.
As for your small pulley, it's not much trouble to try it- only 4 bolts and maybe a vee belt; with your driving style and the roads around your area, it might improve cooling... or not. If it gets hot earlier than you can live with, just remove the custom pulley before you get boil-over. No one can really predict what will happen with any given car combination, but I wouldn't intentionally use a small pulley at long WOT Silver State events or at Bonneville.
Minor face scratches in a pump won't hurt anything; use non-hardening sealer like Permatex #2. Pressures are only on the order of 15-20 psi or less. Just be VERY sure the new pump is NOT designed to run on a late engine with a serpentine belt. Serpentine-belt water pumps are designed to run BACKWARDS compared to vee-belt pumps. Massive overheating will result from mixing this up regardless of your pulley ratio.