If it's an MFi cab (as it sounds like) the original tank and pump will be fine. Everything else will require changing fuel system wise and the loom will need changing too.
Best bet would be to get a loom from an EFi cab and fit a full fiesta RST engine, then use OFAC management. might as well have EFi if you're changing the loom. Then you could even go for a plug and play megasquirt later when required.
Lee
