Frame to bottom of air bag sounds like the Neway axle measurement. Of course if you have the OE manual for your rear axle you can verify it yourself. Or you can download the manual here:
Unfortunately that does not identify the specific model we have, but I think ours is one of the lighter ones. Measure frame to bottom of airbag support (the steel disc under the rubber bag.)
The 7-1/2" - to - weld spec appears to come from a document on the ACA website, for a 2000 coach, sent by Western RV in 2007. It's probably what they used for many years.
Franklin & Dessa
2001 Alpine 34 FDDS
Tow a 2014 CR-V