Until the DECwriter series and the VT04, DEC sold OEM printers and terminals were made by other manufacturers. Paul is speaking of the traditional LP01, which Centronix made (I think) IIRC [Datapoint maybe -- I forget], and it was ordered with either an upper case only drum [faster - as it had two copies of the A-Z set] or an upper and lower case drum - which included some special characters. The 8-bit parallel interface was defined by Centronix, which was the standard printer interface for Minis and later PCs. The difference with the latter is that IBM used a common ground wire so they could put it in a DB25S connector. With the PC, IBM designed the interface using a bi-directional Intel parallel I/O chip so you could read it - which was not true of the earlier interfaces for PDP-8/10/11.
As for the LP01 drum, it was possible to replace in the field but a PITA [we did when we got a used one from Tektronix's Finance shop that was running RSTS Cobol and moved it to the Teklab's 11/70 - V7++ UNIX system].
FWIW: when the Printronix was released in the late 1970s, it became the standard lineprinter for UNIX sites until the rise of laser printers.
As for putting a 1403 on a PDP-10, I suspect it was possible, but it probably took some custom interfacing.
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