Yeah fiesta lump will go straight in but the EFI head will not mate to your inlet manifold and you'll need to remove the core plug from the dizzy end to fit the dizzy.
Going EFI is always a good call as above, but I wouldnt recommend the 20 year old OFAC/B stuff as IME there is always broken wires, sensors and it just becomes a big head ache trying to fault find... I'd go standalone, there's some really good bang for buck systems available these days!