I don't recall ever seeing a 1403 on a DECsystem-10 or DECSYSTEM-20.  I suppose someone could have connected one to a systems concepts channel... or the DX20 Massbus -> IBM MUX/SEL channel used for the STC (TU70/1/2)  tape and disk (RP20=STC 8650) disk drives.  (A KMC11-based device.)  Not sure why anyone would.  

Most of the DEC printers on the -10/20 were Dataproducts buy-outs, and were quite competent.  1,000 - 1,250 LPM.  Earlier, we also bought from MDS and Analex; good performance (1,000LPM), but needed more TLC from FS.  The majority were drum printers; the LP25 was a band printer, and lighter duty (~300LPM).

Traditionally, we had long-line interfaces to allow all the dust and mess to be located outside the machine room.  Despite filters, dust doesn't go well with removable disk packs.  ANF-10 (and eventually DECnet) remote stations provided distributed printing.

CMU had a custom interface to some XeroX printer - that begat Scribe.

The LN01 brought laser printing - light duty, but was nice for those endless status reports and presentations.  I think the guts were Canon - but in any case a Japanese buyout.  Postscript.  Networked.

For high volume printing internally, we used XeroX laser printers when they became available.  Not what you'd think of today - these are huge, high-volume devices.  Bigger than the commercial copiers you'd see in print shops.  I(Perhaps interestingly, internally they used PDP-11s running 11M.)  Networked, not direct attach.  They also were popular in IBM shops.  We eventually released the software to drive them (DQS) as part of GALAXY.

The TU7x were solid drives - enough so that the SDC used them for making distribution tapes.  The copy software managed to keep 8 drives spinning at 125/200 ips - which was non-trivial on TOPS-20.

The DX20/TX0{2,3}/TU7x was eventually made available for VAX - IIRC as part of the "Migration" strategy to keep customers when the -10/20 were killed.  I think CSS did the work on that for the LCG PL.  Tapes only - I don't think anyone wanted the disks by them - we had cheaper dual-porting via the HSC/CI, and larger disks.

The biggest issue for printers on VAX was the omission of VFU support.  Kinda hard to print paychecks and custom forms without it - especially if you're porting COBOL from the other 3-letter company.  Technically, the (Unibuas) LP20 could have been used, but wasn't.  CSS eventually solved that with some prodding from Aquarius - I pushed that among other high-end I/O requirements.

 Tim - care to take a stab at this?