how thick is a '69 flat-top log intake?

[Asa]

specifically, if i was to make an adapter for a 5200, would i be able to drill and tap two holes directly in the log head to give it something to mount to?

pictures/diagrams can be provided if need be, but i'm talking about directly in the center of the head

 

[addo]

My measuring of cast iron logs showed just over 3/16" except for local thickenings. The runners are thinner, by a shade.

If you can slip a little G-cramp in there with a small hex nut taped to the anvil face, close it tight on the metal and measure the thread length. Remove the cramp, and recreate the measurement (hex nut still taped on). Now you can readily measure how thick the casting is.