The IRF510 can tolerate up to about 30V if the SWR is reasonable. I've run the same pair at
28V for years. Expect a lot more power and watch the heatsink temps. More power more
As to current draw it depends on the band and what the drivers will give at that band.
Stay under 4A.
Better replacements. THe RD16HHF is at 10$ for a pair and do not exceed 16V with those.
I could list some other RF stuff at maybe 50-100$ a pair. You are limited in the amount of
drive the driver stage can do and the traces on the board will likely go away at more than 4A.