Is it difficult to determine the positioning and depth of the pockets?
In the case of the Healey motor it's pretty straightforward because the valves are vertical and the only interference is with the exhaust valve over the deck (it would take a very radical situation to have piston to valve clearance issues - perhaps Dougie's motors are that radical?).
Locating the pocket is simply a matter of blueing the deck, setting the head on with a loose exhaust valve (no spring/retainer) and manually spinning the valve against the deck to make a mark in the blueing on the deck. Typically adding an 1/8" or so to the diameter of the mark for 'safety'.
Depth of pocket is determined by knowing the lift at the valve of the cam you want to use. Then measure the distance from the surface of the closed valve head to the head gasket surface + gasket thickness (stock type is typically .040) + whatever clearance your machinist suggests (typically around .040 for this situation). So, if the valve lift is .450 and your measurements add up to .400, then you need .050 deep pockets. You don't want the pockets any deeper than necessary because they enlarge the combustion chamber size therefore lowering the compression ratio.
And playdoh is a nice confirmation before running the motor.
Dave