88 International Ring and Pinion

I have an 88 Interantional in minto condition I purchased for personal use. (Pulling a race car) The gear ratio in the Spicer rear end is a 4.56 and at 55 mph it is winding around 27-2800 rpm. I do not use the low gears beacuse we do not pull enough to use them. I plan on switching the gear in the differencial to perhaps a 3.73 and use the low set gears while lowering the rpm.
Q 1- Where do i get a manual on how to replace the ring and pinion with the specs?

Q2- Has anyone done it? If so any tips?

Q3- called the dealer and they have no clue on available gear ratios. Where do i find what is available?

Thaxnks a bunch for any help you can offer.

Ray