Hi Russ,
as Spud has said, use an engine from a donor car, whatever engine you get , use it, then to change an engine is quite easy really, more so if you use a TYPE 9 gearbox as the zetec will bolt straight to it with a little mod, if you use a cvh for the iva then you have most parts ready for the swap to a zetec....flywheel, starter motor etc etc.......
I,ll stick my neck out here & say if you have all the parts ready...new engine etc then it,d be a weekends work to swap em over
Also, you,ll be quite surprised how "quick " the Roadster will be even when using a cvh / pinto / twinky ( dohc ), lets say you have a cvh engine with approx 80hp..... & a Roadster that only weighs approx 500 to 550 kgs .... thats quite a nice power to weight ratio
sorry if i,m messing up your plans
cheers
andy