I started to do an update to "A very short play in three scenes" but it quickly became a little too long for the update.
First, let me give props to Buds gun shop. I sent emails to both Buds who sold me the gun and Hi-point who manufactured it. It wasn't clear who assembled the package deal and hence who is responsible for the fix. Derek at Buds emailed on Dec 26 (Sunday after Christmas) and explained they buy the package deal from Hi-Point but offered to assist in resolving the problem with Hi-Point.
Hi point never responded but they did answer their phone today. The phone was answered by a realperson(tm) not a voice-jail system. I explained the problem and she answered "I know there's an easy solution to that problem but I don't know what it is. Standby while I connect you to someone that can explain it."
Next human voice on the phone says simply "Turn it over". And patiently waited over my objections how it can't be done. Eventually I unscrewed the mounting screws and the solution became obvious. The rails are C channels but with different lengths on the legs. One side fits 3/8" rails and the other side fits 5/8" Weaver rails. Nice!
He said there is supposed to be some documentation in the box explaining this (RTFM!) but I still haven't find it.
I'm just glad it was an easy fix.