As Bill points out, it’s not necessary to be ‘dead on’ exact so just eyeballing it will typically get you close enough.  If not trusting the eyes, then wire gauges can be used to determine the actual measurements.  The location of the machined groove is in a difficult area for measuring with conventional instruments. 

For myself, 1/16” would be the minimum value for both the width and depth of the groove intersecting the three holes within the center cam bore of the block.  Any shallower than this leaves the possibility of the cam bearing pressing into the groove and further restricting the oil.  Any wider or deeper than this can be compensated for by installing restrictors at the rocker arms.  I have found that 0.078” restrictors installed at the rocker arm supports still provides an ample supply of oil to the top end of the engine.

Lorena, Texas (South of Waco)

Thanks Paul  Will try to send pictures.   Other question about depth of cut,  Its just a guess how deep it is, my bore gauge feeler point will not fit in cut, guessing  .020-.030. Its not a full 360 degree  cut just enough to connect three oil gallery holes. Cos

Thanks for offering, COS. How deep should the cut be, and how do you measure it?  

If you can email me the picture I can post it for you.  pts one two three one at verizon.dot net


54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

Hello Members   Thanks to Ted E I made a tool (jig) to cut center cam bore to connect all three oil holes. Have pic but don't know how to put up. If any would like to use it you are welcome, just for freight and promise it would be returned.  Would not include 3/8 all thread or 2" cut off wheel,` that  would add  freight costs. It is small, bolts to rear main seal retainer holes in block and extents down below rear cam bore.  Cos Oregon