As long as all he parts are correct and in good working shape;
before you align the box onto the engine it's important to make sure the thrust bearing is located in the clutch fork correctly and the fork is clipped over the pivot inside the bell housing, depending on the throw out carrier you may have the oem type which has clips or a machined type with flat machined sides that have no way to permantly fix the fork to the thrust bearing carrier so it's important when fitting the box that the fork and thrust be seated and set back in the bell housing and no desturbed while fitting bell housing bolts. The clutch fork and bearing will feel sloppy in most cases as its not secured to the pressure plate, once the slave cylinder is fitted you should find that every thing seems ok, the slave cylinder will take a little effort to refit and that should ensure correct engagement of those parts.
Given the explaination of why your replacing it I would check to see/ confirm that your old pressure plate is ok.
Every man should have a V8 ute.....with a Chev badge.....and a Southern Cross sticker! Mods? What mods?