waltergallons ST70

Just done a bit of research on internet about this. Couldn't find anything specifically about these particular engines, but there was an article about Honda heads generally. The author said heat the head in the oven to about 130 -140 degrees C, and not to go over 150 degrees C or you might warp the head.......... Also leave the guides in the freezer for an hour before hand.
Now when I did it earlier,I slapped the head in the oven and turned it up to 200 degrees C, but this was from when the oven was cold, and I took it out before the thermostat kicked in. So it might well not have been up to temperature.
So maybe I should put the head in the oven at 130 to 140, and when the oven thermostat goes off keep it in for a bit longer so as to ensure the head gets to that temperature....... then try the freezer trick with the guides.
Whilst researching I aslo read that valveguides need to be reamed to match the valves. I never realised this, so I tried to fit the new valves into the guides, and sure enough they don't fit. They need reaming out !

This is turning into bit of an epic saga. One that is perhaps beyond my capabilities, and I might be popping off to see the friendly local engineer......... Steve

I hate it when that sort of thing happens.
Like you say, probably best to take it to an engineer you does this type of thing all the time as it should save a lot of heartache. It will cost more but at the end of the day you aren't only paying for their time but also their experience.