OP here,
Appears; as per my previous post; that my assumption of the Scorpion EXO-R420 having same internal fit as the Scorpion EXO-R320, was a correct assumption.
The Hi-viz EXO-R320 that I ordered from local dealer on Wed July 5th, arrived on Monday July 10.
I went and picked it up, after work, that day. And it fits the same as the R420 I tried tried on.
Which means I've had the helmet for a few days now. And have used it for a couple tank fulls (500 miles ?) on my Griso + NT.
Looks like I made a good choice.
While the R320 may only be DOT rated. It appears what I saw and read about it online, for it only being DOT rated, may be true.
Which is; Scorpion wanted to keep it's price down by not paying for the SNELL or ECE testing.
It's interior outer shell, EPS, and interior padding; look to have same coverage as their more expensive, DOT/SNELL rated R420.
The only less-than perfect construction I can find on this hi-viz R320.
Is that one of the two forehead vents does not click as firmly as the other when opening or closing.
Otherwise I can find no flaws.
As for it's hi-viz being effective.
I've gotten two compliments on it's visibility.
First; employee at the dealer who sold the R320 to me, said upon my taking it out of the box: "
Holy sheet that's bright !"

At the same time, a couple customers standing nearby at the counter, nodded their heads in approval.
Second, while ridding with it on the following day. A car driver started to pull out in front of me, then stopped when he noticed me.
At the next intersection with a red light, he pulled up beside me, rolled down his window, apologized for almost cutting me off, and said it was the bright helmet that made him notice me.
Personally I think this is a great helmet for only $130 ($119 + PA tax).
Again, thanks everyone for the replies.
--ET