Right 1st off welcome, this has been done many times now to an mk3/4 but not to a mk5/6/7 to my knowledge.
The easiest and best route would be get a sierra rolling shell preferably a cossie shell (gearbox bell housing is bigger for T5 gearbox) and use its floor pan to weld you mk6 escort too.
Engine wise there is many many options all dependant on what you are after and what it will be used for