DEC Professional 350 ROMs

I have some ROMs from two DEC Pro 350s I want to image. My programmer fails to identify them automatically. From the technical manual it would seem that they are two 8K ROMS in a DIP24 package. I have tried to pick some other model of ROM and read them, but I am not convinced I am reading them correctly as a result (top 4K all 1s). Here are the markings. On one pair the ROMs are Motorola and one of them is marked LM8450 254E4 SCM 90448C ID8402 On the other pair one of them is marked: /B8250 MM51264KXL/N 23-115E4-00 TP-03 And the other is marked: Mostek 8252 MK36C25N-5 23-116E4-00 TP01 I know that in all cases the last line is just an ID for the actual contents and the last two have a DEC part number in the penultimate line. I have found that using Motorola MCM68766 seems to read the ROMs from one of the machines and I don't get verification errors when I try to read them back again a few times, although the contents don't seem to have any recognisable strings. Using Motorola MCM2716 gave me fewer bytes (of course), but there seemed to be recognisable strings too. The other pair of ROM chips from the second machine always give verification errors. I don't know if they are bad, or if it is just timing problems given that I am not using the right parameters for the ROM chip in the first place. Can anyone point me at a datasheet that might describe these ROMs, or at least what they might be equivalent to so I can set my programmer accordingly? Regards Rob