Leaded fuel creates a " cushion " between the valve & the seat.
Todays engines ( build to operate on unleaded fuel ) have induction hardened valveseats & stellite ( or sometimes sodium cooled ) valves, to cope with the abscence of lead.
You have three choices:
1. Add lead substitute,
2. Run the engines until you have valve recession,
3. Have hardened seats & stellite valves installed.
It's you call.
I can guarantee you, you will have problems, it's just a matter of time.