A few years back, I bought a 60 with the typical head/manifold leak on the clutch side of the tractor. Happily, I found a NOS head and replaced the old one with that and bought a new manifold as well. Since then, the old head has been kicking around the shop as I tend to hang onto such things for reasons I'm not exactly sure of myself. But as I get older, moving it now and then becomes a chore, and I've decided I need to make decision about fixing it or let it move on to it's next career as a mooring anchor. So, what I'm wondering, what is the limit as to how much can be safely planed off the manifold mating surface in order to make this a functional part? Or is it worth the expense of having it built up and machined?