Hello and welcome on the forum.
This is information you can find in the service manual. In mine it states the following:
All Dodge built Motor Home chassis are equipped with Spicer 70, 70HD or Rockwell F-130-NX rear axles.
Available Ratios are 4.56 and 4.88 on the 70 and 4.56 on the 70HD with 4.88 on the F-130-NX.
For vehicle model application see, "Specifications" at the end of this group
So I would like to recommend to get the service manual for yours as it is an invaluable source of information on everything build on your chassis except the coach. unfortunately you have a 1975 model, and as far as i understand a lot of things changed so there are a few additions available and I can't tell you which ones apply to your RV. maybe Oz of Dave can help you with this?
https://www.classicwinnebagos.com/forum/index.php?action=store;cat=37