I have 2 ways to service valve guide clearance issues in older heads---------If they are worn a little, you can knurl the id -there are different types of knurling tools and a big difference in results. After any guide work I finish hone the id with a Sunnen diamond one pass hone tool.
Valves can be replaced with oversized stems to make up the difference that the service work has made the guide straight and round but will be oversize.

You can use a guided pilot step drill that will drill guide oversize for installing a brass liner and then use a swedging tool and the resizing methods above.

You can drill out the head and install a completely new guide with an interference fit od for either stock or thinner(lightweight) stemmed valves-------and size the id to the valve as above

Guides replaced are usually only .502 od so will need a special size seal.

I looked online and couldn't find anything good about this shop --don't know why anyone internet savvy would of went there-----

Takes about $80,000 of equipment to service cylinder heads----------