Most models have either writing, or an escutcheon plate on the front. The manufacture's serial number tag has a better nomenclature, but we have to look it up. [see
MicroPDP 11/73]
These next comments apply to non-rack based "MicroPDP systems" since I think you would have indicated otherwise were it the case. Comments for prior E.G. - "non-Micro" systems, would be entirely different.
Drives would most likely be MFM type [not RLL], if they were DEC supplied. SCSI is another possibility, but not many were DEC sourced in PDP's but it was not uncommon to see 3rd party controllers and drives in OEM systems.
Most PDP-11's were sold as Controllers in "Expert Systems", and these tend to be the ones that lasted in service the longest, becoming available as these systems obsolesced. Examples could be Phone System Control, Bank Central Alarm Control, Radiological Measuring Devices, Nuclear Plant Control, etc. In these applications it was common for a specially suited interface card to be required in the chassis, but the bulk of the system could be all DEC. As a result these computers are often populated by a re-usable suite of DEC cards and storage.
PDP-11s were made for about 20 years, and the Micro based ones about half that time. The vast majority of the survivors will be the latter, but because they often go unrecognized (or unappreciated) - it's not unusual to hear of situations like yours where they are sold "by the pound" as scrap.
Over that time there will be some 20+ actual model variations, but fortunately for you the final 10 years will probably be limited to maybe 2 or 3 popular standalone enclosures. The BA-23 and BA-123 are the most common in "Floor Stand" form (we called them "Pedestal"). 19" Rack versions of the BA-23 and it's predecessors also exist. For RM BA-23s, the only difference is mounting hardware and cosmetics. They are easily converted.
If yours was a free-standing imitation of a very large Floor PC, then it's likely a BA-23. A quick search of the pages on this forum (or google) will result in lots of photos for you to view. If it is a BA-23, CPUs and memory for original manufacture units will be PDP-11/23, 73, 53, 83, 93 with memory sizes from 256KB to 4M and Disks from 10MB to ~250MB. But externally, they all look the same in a BA-23.
A BA-123 is the size of a small office "personal fridge" [25"H x 13"W x 28"D and up to ~130lbs] and pretty much floor standing only. [we used to say it was a nice coffee table] A BA-23 Pedestal was slimmer and deeper. While it's base was wide, requiring 10", the actual enclosure was 7"W x 25"H x 32"D weighing ~70lbs.
Not sure that helps, since you haven't described it's general size.