So much of the old threads I found are incomplete or never updated info so here is the final answer.
I chose AutoZone because of the lifetime warranty. A little expensive, $40 more but since this is a keeper I may as well spend $130 and get the peace of mind. Yes it is the HVAC for the NA6 90-93 Miata.
Here is the difference but "DO NOT WORRY"......
Inside the housing box it fits like a glove....
Look at the NA8 original......
Once the housing is installed, the return tube is pretty much in place out in the engine bay........
The difference with the NA8 OEM is not significant.......