Have a 88 12 meter with 1000's and #3 drives 1.33 ratio. Have a set of #4's with 1.25 ratio. Anyone tried this?

the 1:25 is going to kill you ... but the drive swap works , you may need 1 inch spacers at the most on a Fountain.
If the #4's are splined shaft ( older style ) then your upper gears from the #3 will fit right in aswell.