The idea of "punching out" the old guides always bothers me. Sooner or later the head will be worn or damaged from this process, and good heads are getting scarcer.
I had the original iron guides bored and threaded for "bronze-wall" inserts.
Those are threaded in, like heli-coils, then reamed to size.
When the insert wears out, you just pull it out and thread in a new one, ream it, and the process begins again.
The insert also holds oil to lube the valve stems, because of it's coils.
Is this the same as the K-liner system? Sounds like a good idea to me, but its hard to find shops that know about it, and do it, in this country.
My queries about cast iron guides have been rendered academic now anyway - the head arrived today and they are bronze - the photos on ebay made it look as if they were iron, but it was just 37 years of grime & dust that made them grey, and the seller didn't say.
I've offered up an exhaust valve from my old head and it sticks within about half an inch in both exhaust guides, so either the guides will need honing or I'll have to get some correctly sized valves. The G&S valves seem to come oversize, ie: .311" stem diameter instead of .310 max. This is the case not only with the old valves (no wear on the stems at all after 13000-odd miles) and the new ones I bought (also G&S). On the old ones, the wear to the tops of the stems was negligible - a visible polished stripe where the rocker adjuster pin has been contacting but you can't feel the wear, and I'd guess it at well under a thou.
The fit of the exhaust valves in the guides was the best I've ever found in any used British engine - a lovely sliding fit with barely a trace of 'rock when anywhere from just open to fully open. Wish I could remember what guides I used! They look like Wassell guides but can't be (I wouldn't have used them).
The inlets, on the other hand were a tad sloppy on the drive side to significantly sloppy on the timing side. Not as bad as I'd have expected at 130000-ish miles, but not good enough to re-use. The inlet stems were correctly sized too, and showed about half a thou of wear.