Talking about the pins being exposed on the back, I had a Tandy TRS-80
It had a connector on the back with all the bus pins - being the geeky sort I bought the correct edge connector and a ribbon cable to connect to it. Tandy even produced a manual with the entire circuit diagram of the computer - where would you see that these days?
Two mods I made to mine
a) from an article in Byte, it turned out they used a character generator capable of displaying lower case characters, but had skipped on the RAM chips, so only had seven instead of eight. Solder in another RAM chip on a 'piggyback' and you had lower case
b) I bought a yea old Teletype printer surplus from the Post Office for a fiver. The sort of thing which I guess was used to send telexes - very, very heavy. Not a KSR-33 or anything, this was solid metal, and used a roll of paper. I typed in a program listing which translated ASCII to the Baudot code the thing talked - and to get the signals out the program tweaked the cassette outlet at the correct rate, which in turn was hooked up to a huge transformer which swung the Teletype magnet.
