The pic is of the air slot created by drilling the air inlet hole to intersect with the main motor housing hole. Jay and I will try this out before the shop machines any more of them . The shop manager and I looked at this one closely today and we were pleased that the housing was not rough in the ID after the undersized hole was bored. The finish honing to size will make this bore even smoother......The shop said it will hold the tolerances...to one half 10 thousanth...I dont think that tight is needed.

Bob, from MPT said a -.000 to a + .002 would be a good tolerance to work with. Note this casting has a 7/8ths slot as it is going to Rick Mammal as a replacement for his original. The rest will have .510 slots  for all you guys like me that will build your own. !/2 inch steel plate is a heck of a lot easier to find than odd 7/8ths. This way you will not have to buy 1" [ way overkill] and machine it down.