You'd probably want to factor in that most bike engines don't last half the kms that a road engine does (esp the ones in very high hp per litre configurations) - and loading them up with a full sized car, rather than a bike (where you essentially get to a couple of hundred kms per hour quite quickly then typically back off a bit) loads them up a lot worse. Expect shorter engine life big time.

There's certainly more than a few mini conversions out there - most of them fwd, but some rwd. The best fwd conversions for the mini (in terms of overall performance - acceleration and handling - potential) are probably the honda engine conversions. Not a dead simple swap, but instantly gets you the power to snot (with a relatively stock honda motor) a full race BMC A series engine

Now specifically on reverse - some of the rwd mini conversions have a reverse setup. what they do is mount a second 'starter motor' backwards. It's electric and there is a lockout switch that only allows a complete circuit when you are in neutral. Basically what happens is you select neutral, then hit reverse (which is usually a button) and the starter engages on the flywheel, and you creep slowly backward. Since the car is light, it'll allow reversing (albeit at a slow speed) up an incline. But you'd basically only want to use reverse for parking, and where there was absolutely no other alternative.

I don't know if that would be legal in Australia, the conversions I've seen on the net are mostly in teh UK.

Another good fwd conversion for minis (and I suppose we might consider them for the fwd dattos if possible) is the suzuki swift engine. They produce decent hp in stock form (even though they are getting on 20 years old or more) . There's a bloke who has an open wheeled racer (I forget the class - if I remember I'll edit/update this post) - I think it's a 'maddox' . They have the option of running pushrod 1.3 litres with massive mods (he previously ran a toyota 3K engine, or they can use the swift engine, but very limited mods (have to run 10.5:1 compression maximum, and I think camshaft profile is also limited, and they are also mandated an 8500rpm redline_). Anyway, the swift motor essentially matches the output of the 3k, but does it at a lower rpm (slightly) and has more 'area under the curve' - more torque and broader powerband, so it's a lot faster than the peak hp figure comparisons might otherwise make

I'll say this - if someone was to pursue it, there's nothing quite like driving a full on NA race engine screaming at high rpms with a very close ratio gearbox to suit it. Takes a driver that knows how to get the most out of them, but once you find that 'groove' where driver and car are in sync, they are fantastic.