Guys,
Thanks very much for the specific advice. Grumpy you have given me a great suggestion. I do am a not a believer in purchasing an expensive tool for a task thats simply not going to bring enough benefit.
I will try the easy out as per your instructions. These example bosses had bolts that were already snapped before they came into my possession. To date I havent actually snapped any bolts as I tend to heat them up and remove them very slowly moving them back and forth until they come loose and break the rust seal.
Mark, I agree with your comments, its not worth spending any significant money as you can pick a scrap mower up for 5-10 and grab the boss off it with a little luck.
I will give it a try and let you know how it goes - I wont go down the re-tapping method as I can get replacement bosses fairly easily and I dont want to compromise the function of the boss in any way - purely from a safety perspective.
Sorry for the slow reply on this issue, been fixing many mowers over the last couple of months as the grass is going mad around Canberra!