I just found in one of my paint books the original engine color codes for engines back to 41, these are the PPG Ditzler code numbers, I don't know if they can be translated into a paint these days as most of the old paint numbers I give the mixers these days they appear to have no clue as to their meaning, their new system of making paint doesn't go back that far.
If need be I can get you the number tomorrow when I am at my shop. Personally, I would just go with the Bill Hirsh paint if you can get it. and yes it would be the Ivory for 54 merc.

55 Vicky & customline
58 Rack Dump, 55 F350 yard truck, 57 F100
59 & 61 P 400's, 58 F100 custom cab, 69 F100, 79 F150, 82 F600 ramp truck, 90 mustang conv 7 up, 94 Mustang, Should I continue?