Engine Top End overhaul

[Saculia]

I have a 93 gs500e, on which I have put 33000 trouble free miles.  Resently, due to some dealer neglect, my bike developed leaky valveguide seals, and is burning a little bit of oil when the enging gets revved up.
I am currently in the process of pulling the engine out, rebuilding the heads, hoaning the cylingers, and re-ringing the pistons.  I am interested in keeping my bike mainly stock, as it has been in the past, so I don't need any crazy port and polish work.
Does anyone have recommendations on what are the next size of piston rigns that one should go with, while doing this kind of work?
Also, I have a slite problem.  About a year ago I had accidentally replaced one of my exhaust bolts with an aluminum replacement.  Now that bolt is broken inside the head.  I don't know yet if it can be extracted with and extractor kit, since the aluminum could have gotten welded inside from the high heat.  Does anybody know if a machine shop could repair this problem easily.
Thanks in advance,
Anatoly

[Blueknyt]

if your redoing the entire top end, have the head done by a shop, (valve job) they can also extract the bolt, OR when you put the head back on, grind the area flush drill and tap the bolt whil in the head for correct size bolt, if the bolt is aluminum then its mostly head matirial by now. do your self another favor, crack the bottom end and do the lower end too, both crank and countershaft bearings. Full gasket kit is only 60$. im sure you will cry if thelower dropped out while you had the chance to "freshin it up" while it was out of the frame. Just my Opinion