Well, the F4U-4 is NOT over-modeled.
As to tactics.. Co-E, Co-alt, the Yak-9U has virtually no chance unless the F4U-4 pilot is a registered dolt.
You must get and maintain an altitude and E advantage to have any success. Your problem is that the F4U-4 does everything better than the Yak.
If you cannot gain an advantage, move on to a lesser target as the -4 will dominate the Yak in every aspect of the flight envelope.
My regards,
Widewing