The under 750cc class (H-Class) was the entry point for many racers back in the 50's and 60's. And for backyard mechanics, the H-Mod class was the place to be. Homebuilt and heavily-modified cars were powered by souped up Crosley engines, Fiat powerplants, and even Panhard mills. A variety of companies contributed their efforts, with Jabro bodies and frames, Devin bodies, and Braje performance parts.
With the growth of vintage racing, H-Mod has experienced a resurgence in recent years. Old cars are coming out of the woodwork and participating in events. (Such as the Reno event held in early 2007.) And information on the cars and the class is becoming more available on the internet. (Tam's Old Race Car Site has a series of pages on H-Mods, there is a Yahoo Group on H-Mods and Sports Racer Net has extensive listings of H-Mod chassis.)