There are a lot of variables. 4.750 is the proper theoretic measurement from the face of the stud to the bellhousing flange (contact surface with the back of the block). If you are using a block plate between the bellhousing and block you have to figure this into the depth of the bellhousing (add .132" and adjust the stud accordingly outward towards the block .132"). Flywheel thickness will also effect your geometry. A thinner flywheel moves the pressure plate away from the ideal contact point, as it moves forward the bearing and arm move forward, causing the outboard end of the fork to move rearward and cause increased pedal travel and effort. So the 4.750 measures to the back of the block because it is a constant measurement that never changes. It assumes you have a stock thickness flywheel. If the flywheel is thicker or thinner than stock you must also disl in the correct amount on the stud for this dimension. GM considers .960" as the "standard" flywheel thickness. So if your flywheel is .860 thick you need to move the stud forward another .100". Hopefully you are using a factory bellhousing, because I don't know about McLeods, but Lakewood are almost impossible to get the geometry correct even with the adjustable stud.

GM has two stud lengths, 1.78 for the long throw out bearing and 1.48 for the short bearing which is what you should have. The Lakewood adjustable stud only provides up to 1.58 length. Barely enough to correct for the block plate and a resurfaced flywheel. The last Lakewood I worked with had .120 deeper than the stock bellhousing to begin with, so proper geometry could never be achieved. If you get it correct with the clutch pedal pressed to the floor, the lower arm of your z bar that goes to the clutch will be pointing straight down. You never want it to go further rearward than that or you start stressing things with it going overcenter. It is okay for it to be slightly short of straight down towards the front of the car.