Apols for the delay - been off-forum.
I replaced the original Steaming/Downlight combo with the AquaSignal Series 41 light purchased from Budget Marine, here in Cole Bay, St Maarten. They did not have a 24V version, so I bought the 12V version, and successfully re-used the old globes - a 25W incandescent globe (OEM p/n 90003) for the Steaming light, and a LED 50W generic equivalent for the downlight (sourced in Martinique last year).
The mounting holes on the new unit made for a direct replacement of the old; but needed to be drilled for the size of the rivets to be used - which were the same as original.
The reason for the replacement was that the old unit had gotten brittle with age, and the tangs holding the down-light into place had broken away, resulting in the bulb for that falling off and going overboard at sea. The new LED bulb was held in with cable-ties in the interim. Rather than go for replacement of individual parts, I bit the bullet and went the whole hog. The cost duty-free here in SXM, and with Budget marine cruiser's discount, was less than USD250-.
BTW, I decided to hold to an incandescent for the steaming light, on the assumption that power will not be an issue when using the engine; using the 25Wincandescents left-over from the change to LEDs of the Series 40 deck-nav lights and mast-head combo tricolour/anchor light.
Hope this is useful.
All the best,