1989-91 360 roller cam engine questions

Do Not. I repeat do Not sink the valves to get the spring height. Use different retainers or shims. They have plus and minus height retainers. And yes standard car exhaust valves would work perfect.
Get a different timing cover.
Thank you. As for the timing cover, is this just because they are so readily available or is there a reason not to do the machining? I do have the proper tools and know-how (that sounds cocky, I don’t me it that way) and feel it’s a good learning experience to teach my son to work with what you have, etc. Though there is one on eBay right now for 65 bucks….