To some extent it depends what you're trying to do.
If you're trying to keep it roughly in period then the crossflow would be the way to go and the T9 Ford gearbox will bolt straight on with the right bell housing, clutch and flywheel. That engine is very tuneable ( I played with MK1 escorts back in my youth) and adding the T9 5 speed box will give you more versatility.
If you're looking to go more for performance, I would go for a 2L (or 1.8L) Zetec with the T9 gearbox. Relatively straight forward and you only need a basic ECU to drive the injection and ignition.
I did install the 2L Zetec in my much later car and it's great fun with almost 160BHP.
You could run the Zetec with twin Webers and just use a simple ignition only controller such as Omex 200 series. Add a BDA style cam cover and you would have a wonderful period looking engine bay.(as in Ford Escort RS1600). If I had a 4/4 from that era, I would love to do that conversion.
However you already have a crossflow engine so T9 gearbox and then go for the twin Webers etc.
