C1, D1, E1 are the 8-bit proms, but it can be populated with 4 bit proms instead (4x 4-bit PROMs per 8-bit PROM)
C1 = ROM2 = /PROM3 + /PROM4 = J0 + J1 + L0 + L1
D1 = ROM3 = /PROM5 + /PROM6 = L0 + L1 + M0 + M1
D2 = ROM4 = /PROM7 + /PROM8 = N0 + N1 + P0 + P1
Unfortunately the M28000 to 2716 adapters I posted for free on OSHPARK need to have the /OEs inverted to be used on super breakout, so those won't work for you.
I did a high score save kit that replaces the PROMs with a CPU plugin, but I never got around to testing on real hardware.