thank you for your quick and very useful reply. the lamp bases for the 2331 have two threaded inserts on the back side which allow attachment to the lamp base. any idea if this is a standard feature on all mfgs. version of this base, or if i need to locate an exact replacement from the original manufacturer
Standard feature, but I believe the two machine screws are in different locations on the white vs. gray sockets. I want to say yours uses the white socket, but am not 100% certain. I have an example of the fixture in question, but sadly, the original socket was replaced with a med. screwbase before I purchased it, rendering it useless as a stage lighting fixture.
if you are using the EGE lamp then the screw hole positions do not matter because the EGE lamp has a spiral filament. If you were replacing bases for a lamp that uses the BTL lamp then you are correct you do need the correct lampholder orientation. You can either drill the base or buy a direct replacement from David Ashton who posts on here as Allthingsthaetre.
David changed his screen name to David Ashton quite a while ago, but I don't think sourcing this part from Australia is necessary or warranted, (unless the OP is located in AUS, of course).
I must admit I have not found a North American sourced lampholder that directly replaces the lampholder used by Strand in their base down ellipsoidals and patt 123 fresnels. I either repair them using replacement centre pins from another lampholder or when required redrill the mounting holes in the fixture. If there is a suitable replacement to save redrilling then it would be good to know which lampholder.
I have a direct replacement for the Strand bases at US$15 each, I only went to the trouble of getting them made because I could not find a low cost unit.