I've got 17 x 8.5 inch wheels on my mk 1.
It really is about as large as you would want to go without some serious body work.
As you've got a 4 door I presume you will not be going with xpack style arches?
You are then looking at at least mini tubs (outer skins) to fit wider than 8 inches (comfortably) and full tubs, (raised arches) to fit larger than 17's or run the thing low.
Depending on wheel offest you will also need to get a narrowed diff, I am running mk1 cortina with mounts moved.
The front end is tricky depending on wheel width and offset. Adjustable caster is a must to get the wheel centred where you need it, even then you may need to trim a bit.
Standard brakes will look lost in small wheels so you will need larger discs.. I've gone 300mm,
Suspension geometry will be out with the front lowered enough so that it does not look like a 4wd, therfore the rack ends need modifying to correct bump steer.
Rear springs need resetting.
Boot floor will need modifying to clear the diff once running low and you will need an larger tunnel to clear the tailshaft.
Chasis rails need notching for bumpstop clearance.
front and rear shocks need changing.
There are a lot of things that will need doing if you want to do it right. Fitting the rim and tyre under there is only the start. http://www.classic-ford.o...px?m=14462&mpage=4