The size difference will not affect the way the pedal feels drastically, it'll probably be a bit heavier & the travel will be a bit shorter. The numbers on the side refer to the internal diameter of the master cylinder, with the one you have now be 11/16's of an inch diameter, & the suggested replacement being 3/4's of an inch. The bigger the number, the more fluid there is in the master cylinder, so for bigger brakes you need bigger master cylinders (on the inside). I've used up to 1 inch master cylinders, I was going to suggest you get the Sunny master cylinder, which is 13/16's, & change you rear wheel cylinders to match. You can get 11/16 & 13/16 rear wheel cylinders, the first for front disc brakes, the second for front drum brakes. If you're doing the master cylinder, it's wise to do the back brakes,too. Be sure to say in a big voice that your ute has a brake booster & disc brakes when you go to the parts shop, because most utes seemed to be unassisted drum brakes, but it sounds like you have it pretty nuch under control. Good luck with the project.