Yes, it can be done, and was one of the ways hotrodders tried to improve performance before the 848 head came along. Recessing the valves is an absolute must, as is putting shims between the rocker arm stands and the head to restore the proper geometry on the rockers and prevent the pushrods from being so long you run out of adjustment. Since the exhaust rockers and valve stems are at an oddball angle, there might be some geometry problems there that simply shimming can't correct.
It sounds like your "machinist" might not be qualified to analyze and correct all the problems the milling job might create, so it's going to be up to you to make it work.
Measure everything, and don't assume anything is going to work right without checking it, repeatedly.
Jerry
