Better control
The "Easy" setup is preferable to the "Ace" setup on several of the shorter courses. Under the Easy setting, you will not achieve the same sort of speeds as you would on the Ace setting, but will be able to keep the car in control and hold your line through turns. Stability is absolutely essential.
Tires
The bias-ply tires on the historical cars burn at a much faster rate than modern radials. You must adapt or risk losing every race. Practice your pit-stop routine until you are able to enter and leave with absolute precision. Also try adjusting the tire pressures during prerace practice sessions to determine which setting gives the longest life. Modify your driving style to eliminate tire squeal in the turns. Nothing slows you down like extra pit stops.