I wouldn't worry about the age of the Nissan motors. SR20's were still being used right up until the latest S15 Silvias and are built as tough as nails. Being naturally a north/south engine & gearbox (like an escort) theres going to much less things to change.
The new Ford motors are all front wheel drive i.e. east/west orientation so you need to then change them to north/south to suit escort, with gearbox/bellhousing/sump/water rail/exhaust and inlet changes.. the list goes on.
As above the MZR is a bit of a waste of time, not too much you can do with them. And using a Duratec is quiet a bit of work to get in (although quiet a good engine in NA form). And if your wanting more power ie: turbo you going to have to rebuild it all anyway really. Its definitely doable, but we're talking major work and cost (don't forget engineering to be road legal!).
F20c, the one main problem is the engine block height, and requiring sump clearance over the crossmember. Something im going through at the moment. So either dry sump or modified sump/crossmember (hoping for the later).
Heres a thread to possibly the nicest nissan engine build ive seen (although used the older FJ motor - but could easily be a SR20t)..
http://www.classic-ford.org/cfp/tm.aspx?m=17599 My build thread.. still early days really..
http://www.classic-ford.org/cfp/tm.aspx?m=54511