vjpcat:
I have acquired an older PowerWheels motor and gearbox from a Kawasaki trike.
Do you have more information than this - because there were multiple Kawasaki Power Wheels made:
http://service.mattel.com/us/instruction_sheets_results.asp?brand=168
The closest I could guess based on your limited information was the "W6214 - Lil Kawasaki" - which was a small, single motor 6V ride-on toy (though that shows it as a quad, not a trike). The link for the 6V battery manual details that the battery has a 25 amp fuse, but the manual for the toy itself says it is a thermal fuse.
So I would say it is some kind of resettable fuse, rated at 25 amps. That would mean (if this is the same vehicle) that your motor can pull at least 25 amps when stalled, possibly more. When running and no load, it probably pulls at least an amp, maybe more. When loaded, you can figure 5-10 amps.
Without measurements or some other details - we'll just be guessing, so you need to do some more research or take some measurements for us.
That said - that kind of a number for amperage on those motors is about correct; they are fairly beefy things. In short, an L293 and 4 AA batteries will not cut it for this motor.
For a battery, you will need basically the same thing the ride on toy used - a 6V 4 aH (or better amp-hour) battery. You will want to put an inline fuse as well (as close to the positive on the battery as possible) - of whatever amperage was originally specified (or start with 10A and increase to 25 if it keeps blowing).
For the h-bridge, you're going to need something beefier - check pololu for something with a rating of around 30 amps (you size based on stall current plus around 20% extra).