You are looking at a couple of issues.
One, quadcycles may not be road legal without being tagged, and insured as an automobile--and you may have to have a driver's license to use it on the road.
If you are planning on putting two motors on the bike (one for each rear wheel) synchronizing them may not be as trivial as you hope. If you only go with one you still have a single wheel drive bike. Two motors also doubles the cost, and two sets of batteries doubles the weight.
The trykit is for British racing bikes and is hand built, it's not going to be inexpensive. Also the trykit shows disk brakes, they are not commonly found on hub motors. It may actually be cheeper to have a custom frame built than modify an existing frame.
Personally I would recommend keeping it simple and just add a rear hub motor to your current frame. If it ends up being inadequate you already have half of the parts you need.
If you are dead set on making a quad, I really would recommend going with a mid mount motor like the stoke monkey (clever cycles makes them). A quad is conspicuous enough. A stoke monkey really isn't going to draw any further attention.
Allen is spot on...
1.) There is no where in any state or country that I know of where a 4-wheeled (powered) vehicle would be allowed on public roads without registering and insuring it.
2.) Trying to power either of the (paired) wheels on a trike requires a lot of work, if it's even possible. That's the reason why most people power the single wheel with a hub or use a mid drive motor to power the rear chain...
Why would you want to turn it into a quadracycle for, in the first place?
P.S. 48v 1000w motor will net you close to 30mph on a trike frame.
P.P.S. No matter how "stealth" a bicycle looks, if you're doing 30mph on it and you're not pedaling, Leo is gonna know something's up.. LOL
Yes, I've heard about the 4 wheel thing being an issue. I wonder how the berg toys company gets by with making their pedal carts? Check out the Berg GranTour. It even has a trailer option to haul the whole family! Would this be legal as long as it did not have electric power?
I wonder if I stick with the 15mp/h rule, it I could do a 4 wheeler?
Reason why I was hoping to do 4 wheeler is because the trike is SO tippy in current config. I remember purchasing the trike on ebay.de, and thinking, this is going to be so stable...and then I rode it for the first time and almost bailed. The only real safe way to ride it is you have to lean it around corners by 2 wheeling. This is fun and gets looks, but with a heavy battery up front (in the luggage area), it will be much harder to ride this.
I mean, you almost can not even ride where there is a slight inline of more than 1% or you will tip over! I guess this is why the design never took off Recumbent are not affected because of their low C of G. I'm not sure I'd want to do 30mp/h in current config!
I know in the motorcycle world, there is ways to get around having 5 wheels, by doing the training wheel thing...but thats kinda child like, though they do make a adult version I hear...?
Well, I've got some thinking to do I guess.
Anyone ever see a crank kit like the one from bosch, but with more juice?
This is the cleanest looking crank motors I've seen, but are all rated to the EU safety limit. I'd be happy with 500W 48V if I could find something.