Engine and gearbox conversion sounds practical too. 
The 2.8i engine & box drop straight in to the 'Tina's from MKIII onwards with next to bugger all modifications needed 
Dropped a couple of V6's into Mk 2 Cortinas, without putting the then 2000E gear box in, or changing the diff, used to like hell to about 90, happy days..... 
Back in our pre children days, we dropped a Tickford 2.8i in to the old lady's MKII Escort (originally a 1600 Ghia).
The doner car also provided the front legs, discs, hubs, etc, along with it's 5 speed box and a few interior bits (seats, leccy windows, etc).
Final drive was courtesy of an RS2000 axle reworked for a 3:1 ratio....and it was an absolute f***ing animal

Sounds fantastic
bet you wish you still had it, still we have all been there, sadly......

I'd love something mad like that as a weekend toy again, unfortunately the mundane things in life such as kids, mortgage, etc have taken precedence.
You know what the mad thing is though?
We did that mod for the missus when she was 18 (1992) and had just passed her test, and the insurance company didn't really bat too much of an eyelid when the mods were declared.
You phone any insurance company up now and tell them you've made those kind of changes, and it will be a wonder if you ever get insured at all (even now we are middle aged).
Pretty much all the fun is gone these days, all we have now is people suing each other because they've been offended or hurt in some way :-/