Welded-on kickstand plate, flimsy chainguard attachment tabs, and a stamped-steel, tack welded seatpost clamp. Probably a 1" (25.4mm) seatpost, correct?

I'll wager even money that this is a 2010's Huffy Santa Fe or variation thereof. Beware of forks with brittle steerer tubes on these - it is not a bad idea to swap out the unicrown forks for something else. The rear triangles are often way out of alignment too, so if you're doing a custom that you care about, put a Park frame gauge on it.

If you don't have a Park alignment gauge, there's always the string method (not great). I've never tried it before, but you could take a household laser level, line it up with the top tube, and then measure from the laser centerline to the left and right dropouts to verify.

-Kurt