step one is to strip the components off the frame, and then using water as hot as you can bear and some good detergent get washing, then any really rusty bits wire brush. No holes and it hasn't fallen apart?
Good, go from there!
There are guys here who can make you decals up from old pictures, there are frame builders who can repair and modify and to be honest where you stop is up to you. The only limits are your over draft and imagination!
Somerset, like 'Heartbeat' with newer cars!
Retro MTB: 1992 Cannondale 3.0 Deore XT M730. 1992 Marin Pine Mountain Deore DX M650.
Retro road: 1992 Eddy Merckx Corsa Extra Telekom Shimano 600 STI. 1993 Dyna Tech Ti.
Modern: 2006 Wilier scandium Ultegra 6600. 2014 Wilier GTR Ultegra 6800.