You can buy a engine at a pick and pull for a real good price. This way if you have the time you can pull the engine out and learn how to put it in as the reverse of pulling it out it could be a good project to work with your son as a bonding project. If you don't have to have it quick, and save a pot full of money. I taught my son how and learned myself was a fine bonding experience. But best of all after all the cut knuckles,bruises there will be no more hot rodding and proud feeling to accomplishment together. And at least a grand more for work on the bikes. Try it you and the boy can doit. atry it if you have any problems you can pm i will give you my home number and walk you through it. Good luck and have fun doing iyt.