55 GLASS TOP. I'm going to answer your question in a different way. The machine shop's information that your engine's deck surfaces are true and will not be an issue in sealing the cylinder heads may be quite true. The use of the newer composite cylinder head gaskets assures the sealing of head gaskets compared to the steel shim head gaskets used by FoMoCo in 1954 - 1964 in y-block engine production. Consider having the engine block squared to assist in accomplishing uniform performance (compression, power) from all eight cylinders.
Those that have had Ford y-block series engine block decks squared have reported inaccuracy in their as-originally-manufactured blocks. These inaccuracies can be:
- the two deck surfaces not being at 90 degrees to each other
- the two deck surfaces not being the same height from the crankshaft center-line
- a deck surface height dimension from the crank center-line varying from the front to the rear of the block
Consider having the engine block squared by decking and having the engine rotating assembly balanced to assure the smooth operation and longer service life of the engine assembly you're putting time and effort into assembling.
Hope this helps.
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York