67 dart 360 conversion help!

There's nothing wrong with the 904 Lock-up style transmission. Gasket set, friction plates, steel plates, bushings, etc. have been the same for years, be it a lockup on non-lockup transmission. In '92 they went to a wider front band. Anything you want to do to a 904 non-lockup can be done to a lock-up.
Converter wise, there are lots of performance lockups being made by a large number of performance converter builders. The diesel boys use lock-up converters and we all know how much hp and torque these guys are finding.