I would pack the head up and ship it to Mark DeGroff. tel. 818-701-5274
Mark is the most experienced shop there is for this (and similar) heads. Too bad CA is on the left coast but hey you could ship it greyhound they aren't not too expensive.
Mark could turn down oversized guides or ream the holes where they fit if the openings were getting elongated and press them in an either way an experienced shop will do just what they see as the best option. Aluminum is easily reamed out but since your dealing with an aluminum head you basically have one shot at doing the job right so you want to find a good machine shop!
This brings to mind a bad experiance.
I remember a head from an '85 300TD that I bought, the seller insisted that it had been rebuilt with new guides. Long story short is that on a cross country trip it started using copious levels of oil and my blow by went up suddenly. It was a huge dissapointment! I left a smoke trail all the way from East Texas to Calif!!
I had to pull the head and have the job done right because the previous shop had used brass guides and one was wallowing around in the hole, it was fortunate that in the 5000 miles or so that I put on that head it didn't work loose and destroy something.