What RPM going through the traps with a 408?

My slicks are 26/8.5/15 M/T Et Drags and im running them on 7 inch wide steel wheels with no tubes.I have had the best 60 foots with 15 psi in them.14 or 16 psi doesnt seem to work as well with my cheapo setup .Im tempted to stick a 100 shot of spray on it and be deep in the 10's ,but i want to do it with just motor ,just so i can say i did it with a 10 to 1 all motored small block.When this motor need freshened up (if it ever does since i dont run it much) im gunna do sum head porting ,more cam ,and carb ,but i just cant bring myself to tear down a healthy motor thats stayed together for over 120 passes and running faster all the time.Mines just a Nostalgia event racer that is not street driven.Its only raced about 6 or 8 times a year at rare 64 and older events,so it may never wear out ,lol...