sounds like you got a good setup, just need a good reliable motor..
for 1500 you should be able to get some cylinders ported, a head, pistons and a new 4mm crank.. thats what id concentrate on first..
then if you have some money left over you can probably find some used carbs, intakes, and reeds..
id start pricing the porting, head, pistons and crank from a builder and see where you are.