Firstly, well done on the great score!
Definately listen to Joe Aichinact. He has one of the cleanest 200b SSS Coupes in the country with very tasteful mods.
Do not butcher it. Do not cut a hole in the dash to fit a modern stereo. Do not put an SR in it. If it is as clean as you say it is then it'll be a rare find. I sometimes wish I had not done an engine conversion in mine but what is done is done.
Sorry to give you a hard time. I know it is your car and you can do as you please. I get a little passionate about the 810 series. Especially the SSS.
Best thing to do is give it a good wash down everywhere. Clean in the door jambs, under the boot lid etc. get it up on stands, take the wheels off and have a check over all your brakes, rubbers, shocks, hoses etc. Buy new spark plugs, replace all your oils, wiper blades etc. Get your radiator flushed, replace your top and bottom hoses, coolant, fan belt, thermostat and water pump.
Clean up all your earth connections just to make sure you get a good solid circuit with all your electrics. You will have some earths on the lower side of your battery tray. Remove the bolt, make all the contacting bits shiny again and screw the bolt back in.
Oh, remove, clean and regrease your front wheel bearings.
All this sounds like a lot but it really isn't. They are very easy to work on and parts are cheap. If you do these things right fron the start, it'll give you a good baseline on how the car and engine, gearbox etc run. They are very reliable cars. The only real pain you will have is the standard niki 2 barrell carby. They suck. Plain and simple. Biggest problem with is they get vaccume leaks and the larger secondary butterfly does not open. This will make your SSS about as powerful as a peanut.
Anyway, I'll finish now. Seriously, it is worth treating well. You'll love it as it is different and not a 1600. Plus, it sounds like it is the same colour as mine so it must be awesome
Need help just ask. Oh, we need pics!
Cheers Scott