I was able to run those speeds before my engine build. When I tore it down it had standard bore pistons in some very sloppy holes... 20 over at the bottom and as much as 40 over on the top. After the rebuild it does run much better, but I didn't gain any speed, just a little quicker getting there. No upgrades at that time. A good bore job and valve job. Careful assembly.
Check everything. Timing, valve adjustment, carb, plug wires, plugs, points, etc. Make sure everything is operating as it should. Then make sure you can stop that thing.
I do run 8.25 tires on the back as well. That also helps a little with top end. Also know that your speedometer probably isn't accurate. Mine reads about 12% slow.
