As well as straightforward repairs, we also develop modifications to allow the fitment of alternative parts where the original is no longer available.
Marconi 2955 
One such item is our replacement ovened crystal reference oscillator module for the 2955. This replaces a failed original and drops straight into the original footprint. The only modification needed is to replace a resistor with a wire link, or simply bridge it out.
One of the other issues with the 2955 is that the line output transformer (LOPT) fails and is no longer available. The LOPT supplies the EHT to the CRT as well as various auxiliary supplies and (in the case of the 2955) the vertical scan drive.
Whilst others have successfully transplanted an LCD into the 2955, it is recognised that some prefer to keep the original CRT look.
We have managed to graft in various LOPTS from other small monitors, such as those used in the older ATM's, but none were available in sufficient quantity for it to be worth developing past the experimental stage, and with the decline of CRT displays, they are only going to become harder to find.
As a result, we are currently working on a complete replacement AC1 board for the 2955 series. This separates the scan and power supply requirements with a custom wound transformer running at a much higher frequency than the original to generate the auxiliary supplies and an EHT overwind and tripler to generate the final anode supply. The vertical scan is driven by separate circuitry. 
This is still a work in progress, but is looking promising.
Update:  The replacement AC1 board has been put on hold with the introduction of our very popular replacement LOPT kits.