Hello and welcome to the site!
I would suggest that with this small of a machine that you keep the choice of engine/trans very light in weight. Extra pounds are a snow cats enemy, and it is easy to let one's imagination get the better of logic and reason in these machines.
Compare what is availible with what was original eqptment by weight, and try and stay with what the platforms designers engineered it for. They knew about the balance of weight front to rear as well as total weight. A very nose heavy rig is what you are trying to avoid.. as well as one that is too heavy for the running gear.
Looks like a very fun project. Don't be afraid to ask questions, lots of experiance here on this forum. And troll the threads as you have been. Boat loads of good advice, and opinions too. I spent hours here before buying my machine. It has paid off many times over...
Regards, Kirk
We have done quite a bit of research first. We believe the original engine weighs about 180 lbs and made 20-30 hp. This engine weighs approx 260 lbs and makes 80-100 hp. For some perspective A 1600 vw air cooled weighs in at about 215 lbs. So we've added 80 lbs so far. Keep in mind the model after this ran a ford v4 from the factory, anyone know the weight of these with the cast iron clutch assembly? Then of course the 5speed trans, however this has an aluminum case and is probably similar in weight to the 2 clutches, belt drive and shafts that we removed. So let's say with the rad, fluids, heater unit, and clutch pedal we call it 175 lbs added, I think that's a good sacrifice for 4 times the hp, reliability, and extra gearing. Most of the imps I've read about everyone complains about lack of power. Do you think the engine should be farther back?
With this wheelbase (considering track's length front to back) looking at the last picture, I would position the engine somewhere closer to the area of between the seats... IMHO (yet understand that there is not much space to do so...