FYI: "Resin Casting Specialties" was the name of Harold Bradford's first company. He quit because the early resins made him ill and he passed along his molds to Norm. When more benign resin products became available he started a new company calling it Historic Racing Miniatures.
David, yes the kit includes both engines which I believe are intended to be McCulloch sometimes refereed to as Macs. I was told be a former kart racer that twin engines would put you in the "Open" class.
The AMT go kart from the Round2 issue of the '60 Chevy pickup. Made a few changes along the way including:
added throttle and brake linkage
wired and plumbed the engine
modified the seat & pedals
added steering linkage
custom front bumper