I've been exploring many options for my escort. The SR20DE looked good. The S15DE has the same power as an S13DET! More reliable, less cost etc.
The guys at extreme custom engineering will get the motor & box fitted in an escort shell for a very reasonable price.
I'm thinking along the lines of where I'd ultimately be satisfied in terms of power. Pinto, power but an extra 30kg, 2L silvertop zetec can be picked up cheap ($400) but the conversion bits aren't cheap and the power is moderate.
A 20V 4AGE would be my pick. The RWD conversion has been done so many times by the KE70 drivers. Tried and proven. And there's no denying toyota make great motors.