I might be wrong, but I seem to remember that Phase III had an over the counter F1 chassis for sale at the time that used their universally used motor bracket.
Tony P was on the scene on the east coast at the time so I'll defer to him for confirmation.
At the time (late, late 60's/early '70's) I thought these anglewinder F1 cars would take off, but the unlimited CanAm class of cars was evolving to the high powered, steamrolling behemoth it became and there just wasn't room for additional classes. At the end of the day they really did look like fun.