drain oil and take your clutch side case housing off, this will give you your best chance for alignment due to it being machined flat over a large area.
the machine shop will use parallels so its supported on the machined face of the cases. then, they'll just clamp it down and punch thru the new size for the pivot.
i did mine on a Bridgeport, which was WAY better because you can dial in the hole so its perfectly centered. you just barely touch the drill bit to the existing hole and see the shavings, when it peels off the same amount all the way around you are close enough. you could also use a hole indicator but its slightly overkill, your choice.
