Motor mount kits
The hardest part of making an electric skateboard is mounting the motor to the trucks. There are a number of methods of doing this. Welding, clamping or pre made kits. The electronics, motor, and drive chain are relitively simple compare to the mounting
These easiest (but not the cheapest) way is to buy a motor mounting kit. So far these guys are pretty much the best option for this: http://www.aliendrivesystems.com/
They’re kits include the motor mount and the large drive week cog to fit in the Abec 11 wheels. Information about it here
They have all the information you need about using their kits and suggested electronic speed controllers etc here: http://www.aliendrivesystems.com/whats-required-for-a-diy-build.html
LeGrange Trucks is the other option: They had a failed kick starter project (mainly cause they were overpriced and unlucky timing) and theyre sell off old stock on ebay. your going to need to google this.
http://diyelectricskateboard.com/ ay $225 plus postage for a kit this is a good price considering it includes two paris trucks which are great longboard trucks.
Some other people are working on mounting kit solutions so will be sure to update this.
http://www.enertionboards.com These guys are doing kits to if you care to check them out