Are we talking mk2 escort 1970s or 1990s rs2000? If it is a newer version I would start by buying a 4x4 rs2000 as they did make them and the floor pan of that would be roughly same length as escort Cosworth...I would buy a cossie shell though.

If you are talking mk2 then I would fit a mistubishi evo floor pan and drive train...that would be far cheaper without the cossie tax and much stronger with a much bigger parts supply.