gear setup for a mid 80s road bike

[imperial21]

Hi
I am just crossing over to having a road bike and mountain bike, I have just bought a Raleigh Quassar from about mid 80s.
I want to update the gears to a indexed system, Do people have any suggestions ? The bike is 12 speed, I will be buying the parts used as i need to keep the budget low as posible.

 

[Ian Raleigh]

I'd go for a simple but cheap Shimano 105 or RX100 index set up, simple but work beautifully.