Without being familiar with the canadian market it's hard to tell whether it's a good deal or not. In the states I would say pass for that price, but that might be good for your market.
Depending on the source of the rumbling sound it may or may not be a solid car. I honestly wouldn't bother with a motor swap. It'll be a headache that really isn't worth it. Either plan on forced induction, or wait for 6 cyl.