Run like the wind B-Spec and win the Toyota 7 that is the cheapest and easiest way.
The Challenger can do it but you have to drive it hard. Bob won't be able to pull it off in that car.
Yes I did the Historic A spec races in a 1970 Challenger RM, it took extra mods (like Racing softs, adjustable LSD to do it and even then with setup changing it still wasn't easy but I managed.
Much of it depends on the lineup, a 2J up the front and you're toast. Oh and yeah, B spec has no chance.