I now have the rifle in hand and I've ordered the DNZ mount for the short-action Howa. Went ahead and got the tallest of the three, and made for a 1-inch tube.
The rifle -- I'm liking it a lot. The trigger is very impressive for a budget rifle. It's not a particularly "light" pull but it's an amazingly short pull, entirely free of creep and with zero over-travel. I have a Timney Sportsman trigger in an old Mauser and I have a T/C Contender with a very nice trigger, so I've got a basis for my observation on this one.
I'm looking forward to the arrival of this DNZ mount and I'm glad I asked you guys here for assistance.