as Clive said has it had a good service history ? has it been thrashed and abused ? saying that they are a strong motor. 60K is not high mileage for them. if its cheap enough buy it
can't say ive ever had a problem with a worn seat as a new valve fixes the issue. but ive heard of people using some sort of abrasive or cutting tool to clean up the edges of the hole in the seat. might be worth a try ?
are you sure the seats are worn ? the needle (float) valve has a rubber tip so generally its the tip that wears not the seat. have the carbs done a lot of miles ?
we know OEM are probably the best if you can afford them but their are some after market Japanese made parts that seem to be ok, but cant remember the name of them right now
I think your gona need some heat Toni, might be seized on the dowels !!!! can you remove the cylinder head studs ? it might help if you can get em out.
it could be the float valve tips are slightly worn and weeping a wee bit, or maybe the O ring on the valve seat. ive seen the O rings go hard over time and start to crack.