Welcome to GrayBeards there One Eye Joe.
NEF/H&R makes 3 different recievers 1- the rimfires 2- the SB1 receivers and 3-the SB2 receivers.
The SB1 is mostly shotgun(minus the 10ga) and muzzleloaders
The SB2 is mainly for centerfire cartridges. These are built stronger to withstand the higher pressures of centerfire cartridges-270, 30-06, 243. etc...You can send back these to NEF/H&R to get fitted for any barrel except rimfires.
And the Rimfire receivers are only for rimfire barrels only.
As far as Ultra, Survivor, and Handi models go...they are all the same receiver. The Ultra receivers have just a tad nicer finish on them.
Barrrel length and weight-standard, light weight, or bull barrel, are all designated on the website and catalog. The choices are yours my friend.
Simple enough?