S1 has the Ford ST 220 engine & the Getrag gearbox from a Jag. 230 bhp. S2 has the Escape engine and lower BHP at 205 plus a transit gearbox. at some stage the power went up to 226BHP. S3 is the 3.7l engine.
The best is obviously the S1.
Thanks to all for the contributions and answering my question, particularly John for the clear explanation. DaveW I've just ordered your book on Amazon. Reg