recommendation for an easy to adapt ARA motor?

[fovea1959]

"more power Scotty": our bridge arm does not have enough downforce. Part of it is gearing, part of it may be we need a more powerful motor than the PG71 we are using.

We've pretty much gone through all the slow speed motors available to us (used both Window motors, the PG71 does not seem to be cutting it). A highly stepped down banebots or Andy Mark planetary may work also, but I'm thinking about doing a chain drive from an ARA available motor.

Does anyone have a recommendation for a particular automotive motor that would be easy to adapt to a #25 or #35 chain sprocket or Gates sprocket?
("the driver's side van door motor from a 1959 Cadillac has a 1/2" output shaft..."). We have 3 weeks to next competition, arm assembly is out of the bag as part of our 30lb withholding....

We don't have decent machining facilities... we *do* have a pile of the old shaft adapters from past year window motors...