Measure your valve clearances without the springs, and make it easy on yourself. When you're ready to put the springs in, get the hook in the rocker, insert the shaft, and then use a big flat blade screw driver to pry the straight end behind the catch in the head that holds it in tension.
Megacycle, and most places that carry their rockers, maintain an inventory of them. Chances are, those are not his rockers that were reworked, but a set that were exchanged previously and reworked at their convenience.
When re-installing, you don't have to tighten the springs, just put them on and keep them loose, so its easier to get the closing shim on and off (since you'll have to re-shim the entire motor since those rockers are NOT your original ones). I took a long straight blade screw driver, cut a notch in it that was the same width as the spring as a tool to push the spring back, it works well. Once everything is shimmed OK, then you can tighten the springs and you'll be done. Intake/exhaust, doesn't make a difference which one you do first. I personally do this work on a bench (IE: remove the heads), but IDK if you can do that or not, takes a few special tools and there is more to go wrong.