I've got the AJR carrier, get some loctite too if you go with this
resetting the ride height isn't too challenging as long as you have the right tools ( heat gun was used a lot to loosen things off!!), take your time, and take a measurement before you do the sprocket change to set it back to with the new sprockets. I did this in conjunction with the guide on Section8's site.
My recommendation of 40 teeth was based on the fact that I'd forgotten the R runs a smaller rear than the rest of the 748's.
Although some say a 10% change is needed to feel the benefit, it really depends on what you want to achieve as each track may require different gearing.