Does this build sound legit?

NorthStyle

I'd say go check it out... worst thing is you waste your time. I don't believe that everything not made by a well-known manufacturer is bad, rear mount setups are not inherently garbage, and having a built block doesn't mean you need to run ridiculous power levels.

Check out the car if you're really interested. Ask for receipts, compression/leak down tests, maintenance history, etc (like why it needed a new transmission). Purchasing a non-factory boosted car has its own set of risks on top of being a previously modified car, which comes with its own set of risks on top of the risks of it being a used car (risk-ception?). Make sure you're as thorough as possible when going over it and not letting the seller sweet talk you because he's trying to make a deal. If you're unfamiliar with Zs or even boosted cars, take someone with you who is so they can spot the things you might miss.