If the rear tires are not out of balance pressure wise then one of your cross members are slightly twisted. You can check this with a straight edge. To realign it you have to cut the old cross member out and replace it. I did my dad's tractor last year.
Weight is key to a back blade doing what you want, so the heavier the better. You might have to add weight to make it dig in and cut the dirt. I have a #950- 7 foot, 6 way adjustable blade that I love. Adjustability is also something that you'll thank yourself for later.
Retirement is wonderful, but I find that I still work for someone, my new boss (the wife) is harder than the one I retired from lol. I love it just wish I could have done it before my body wore out.
Has anyone seen or done a study on off road diesel and over the road diesel to determine if one causes more frequent regens? Inquiring minds want to know if there's a difference.
I vote no on the spacers and yes on the fluid in the tires. The backhoe alone is sufficient ballast but without the hoe you'll be light in the rear. Fluid combined with a decently heavy implement will help take the place of the backhoe.
Spacers add additional stress to lighter weight axles...