A little history might help. When the 300 was introduced many arilines had large fleets of -200s which had conventional instruments.
Some went for the all EFIS version, but others such as BA wanted their crews to be able to either fly both types or switch easily from one to the other so Boeing offered various options.
One was EFIS plus conventional ASI and engine instruments, another was EFIS plus conventional ASI but with tv screen engine instruments. I think it was very much a case of mix and match.
By the time the 400 and later series were launched, then the aircraft was modified in many ways with new hydraulic systems (one electric and one engine driven per system, rather than one with two engine pumps and the other with 2 electric), new electrics with 2 batteries etc. etc.
Whilst options were still available the variations were probably less.
Many of the 300's still flying now were these early hybrid aircraft and depending on who first ordered them the layout will vary, both in instrumentation and autopilots etc.