You might find that a 2.8 Capri diff at 3.09:1 may be a bit tall geared for what you're putting under the bonnet - might be easier throwing a complete Mk2 Rs 2000 axle in, especially if you're giving it a 5 speed box as well - it'll have a decent top speed on the Capri diff,but acceleration will be a bit lacklustre when compared to the Escort unit - it all depends what you're after out of the car - a pokey high speed cruiser - or an animal off the lights?