Hello Robert,
If you have the Speedball upgrade, and no parts were changed on the board that feeds the 6080 (which seems very likely), then this will basically set you back to the ideal stock voltages, so there should be no issue.
The 6BX7 and 6H30 are very, very different tubes. You would need different sockets, so the question of rewiring the heaters is the tip of the iceberg. I would also expect to run less current through the 6H30 with a different cathode biasing arrangement.
-PB
