I have a P-40 Warhawk with an OS LA 46 in it and it is inverted,i had a devil of a time to get it to run passed a half tank of fuel but i found that it was over heating and cut a hole on the bottom of the cowl and had no more problems.
As far as starting it never had a problem there,also my fuel tank is even with the carb and on cold days run it rich.
I just got done with another Warhawk but this time it will have an OS 70 FS in it and retracts it should be a screamer!
Good Luck!