The Datsun 1200 engine makes a great easy conversion. Ive done two of these conversions so far, one was a standard 1200cc engine and the other was a 1500cc which I warmed up and fuel injected.
Basically you need to get a datsun a12 engine which is complete, and the gearbox (4speed, model 56a is the easiest to fit IMO) and also the driveshaft which if out of a 120y or b110 it should bolt straight up to the morry diff.
Items you need to custom make:
~ Engine mounts
~ Gearbox mounts
~ clutch cable mount
Thats pretty much it apart from the normal exhaust, fuel, wiring etc differences. The coolant passages are close enough that you can use the morry radiator. One thing I do recommend is you find a water pump and its pulley off a a15 engine as they are shorter than the a12 models and give you that little bit of extra room which is good to have.
On the car you need to make a small cut-out on the front crossmember to make room for the engine's front crank pulley. Its possible to install without doing this but the engine wont be in an ideal position. You also need to cut the seam off the chassis and weld back up where the oil filter is to make room for that. If you position the engine correctly you wont require any cutting of the bulkhead and if you get the engine low enough you will be able to use the heater outlet at the back of the head. If you dont get the engine low enough then the bulkhead will get in the way of the pipe fitting.
When you do the conversion it is relatively important to ensure that the back of the gearbox sits at about the same as what it does in a morry minor ±10mm to keep the correct universal joint angles and so the driveshaft doesnt hit anything, you need to take this into account when making your gearbox mount.
If you use the 56a 4-speed gearbox you will need to cut/grind the reinforcing rib off the top of the bell housing to clear the steering rack, and you will also need to shorten the clutch pull lever for the same reason.
I think i have covered most stuff, if you go to
www.morrisdownunder.com then into the forum, Mechanical/bodywork then theres a sticky for fitting datsun engines which includes some good pictures. Not all those conversions in there are perfect in the way that some modify stuff that isnt necessary but its good to bounce ideas off. Ive used ford escort engine mounts both times but I wouldnt use them again as they dont provide enough flexibility for fitting the engine exactly where you want it and the angle is a couple of degrees off which stresses the rubber