Did you see that someone recently had a huge supply of systems for sale and one was a model III or 4 in a model 1 body?
Here's the link on cctalk to the person selling the trs-80s in VA. This is his reply that I missed about his Model 3 in a model 1 body (I'd love to save it or buy it just to see it lol but I don't have the resources right now and I'm not sure if he's willing to ship in the US). Either way, heads up that if you're in the VA area he has quite a few systems he's looking to sell or offload.
Oh I have PDF's of the Tech Manual for Model 4 dated 1983, One dated 1985 that mainly deals with the Gate array version and a Model 4p tech manual. Regrettably I sold my tech manual a few months back.
I have been using them a lot lately to fix my Non gate array which has a nagging video problem. Sometimes get a clear screen sometimes filled with garbage. so still fighting that issue. Thought I had it fixed but it keeps coming back. I think it's haunted.
As far as drives go get a couple of good half heights and use them. Or do as I did on my Gate Array replace with 3.5" drives.