Ian
I up until next week sometime work for a company that supplies these, they are usually seen in a lot of architects offices here in Oz, mainly used for printing plans and such cad drawings and all that hyper accurate stuff, from what Ive seen they might actualy fit the bill for what you want, they print on films and vellum paper. I ended up buying an photocoper with a printer box add on, it prints out on A3 which also prints onto agfa film I use for my screens, which is enough for what I do, plus works as a fax copier and document server, just another thought, Ive seen a lot of 750s and 65os here on ebay, I "think" youd be okay with them, but dont bother trying to contact hp you get put thru to india where they just take you number and someone is sposed to call you back, Ive waiting 3 weeks and still no calls, but thats outsourcing for ya.
Let us know how ya get on with this one...
Steve