Original motor?

I know this is probably a dumb question but I figured I would give it a go anyway.

I was looking at this same 1991 3000GT SL with higher mileage. I test drove it for the second time and everything seemed to check out fine. But only a few things wrong, minor though.

The A/C doesn't work but I'm assuming this would be a simple recharge to fix.

The flex-pipe is starting to unravel so the aftermarket exhaust is extremely loud and the car seems sluggish because of this leak. Wouldn't I just need a new downpipe?

When I took it to a mechanic, he noticed the "junk-yard" writing on the side of the timing belt cover. He said "I wonder if the motor was replaced?" Well with that, the valve cover doesn't look well, original. I looks like the stock ones but only just a tad smoother and it has a really metallic soft blue to it. Hard to notice but definitely not the stock dark black valve cover.

First thing I planned on getting for the car was a full tuneup. But I was wondering if this was a sign that the motor was replaced? If so, I'm guessing the motor doesn't have as high of miles as the car does.

im almost positive my original timing belt had writing on it