The dimensions of the 7 Digit LED display look pretty close to a bare 16x2 LCD.
I could do a uC driving a 16 x2 LCD (using line 1) to replace the LED digits to display the 7 digits with correct postscript text, like ####### Mhz/uS/nS etc. It will also knock out some of that high current LED synchronous switching. They produce a lot of transient edges.
That leaves line 2 to always display both A and B trigger level set points, 12 bit accuracy, should be ok.
Shouldn't be too tricky, just yank the 7447 BCD to 7 segment (U780) and the 74145 (U755) BCD to decimal digit scanning display driver and jumper direct into those sockets. Tap into the decimal dot drive jumper, the nS, uS & mS Led drives and the mode selector rotary switch then remove the LED panel and replace with the LCD.
In fact, looking at the main-board layout (A1,B1,C1,A2,B2,C2 grid squares), U755 and associated common anode resistors (14) & 2n2907 transistors (7) can be completely removed and replaced by the uC PCB socketed into the U755 socket for power and signals and feeding the existing LED com. anode. digit jumper currently fed by the common anode transistor collectors.
The 7 common anode drive lines are repurposed for the 16x2 LCD using 4 bit mode. So that's convenient, being able to reuse the existing jumpers to the display board without mods. Only the Gate LED will remain as OEM.
The Mhz/us, Khz/ms and nS LEDs will all be made redundant by the context sensitive LCD display. Should be able to display the ratios & event counts etc. using proper terminology as well.
Certainly a lot better man machine interface plus less transients & current draw.