a h190 is definitely the go,but drum to drum length will be a problem.the only h190 housing narrow enough is out of a 520 ute,but is a 6 stud axle,& they aren't exactly common.easiest to find will be a nissan gazelle,though you'll have to remove all the mountings.you can also use the diff out of a c22 van,with the a15 motor.these come in alloy 4.6:1 ratios or steel 4.1:1.don't worry about bluebird wagon housings,as these are much too wide to fit under a 1200.with a ca18 turbo,try for the gazelle housing,as these have bigger axles & spider gears than the c22 van,which are the same size as h165 axles on the c22 diff.you then have to run front wheel drive offset wheels on the back to bring the wheels back into the wheel well.you could also run flares.hope this helps.as for opening the falcon boot without the keys,can you get into the cabin,as later chooktins had openings into the boot.if all else fails,an axe can be helpful & phaeraputic at the same time.