Converting 80s bike to indexed shifters
Stick with the friction shifters. Changing a non indexed bike to index is expensive and unnecessary. 

You will need a new dérailleur to index correctly along with a rear wheel that can mount a cassette (assuming your running a freewheel). You will also need new shifters which if your running a road bike are very expensive. 

If you must have index shifting I would recommend a late 90's bike with index shifting already installed. They are generally very cheap second hand and don't require a complete overhaul.

I have an old 80s Apollo road bike that I use for wet weather commuting. I was thinking of doing the same thing and upgrading to indexed shifting. I installed new wheels (Mavic Aksiums) and added a seven speed cassette to the rear hub. I stopped there because the bike ran brilliantly. The new wheels are much lighter than vintage wheels and the hubs are much smoother. A worth while upgrade.

You will get used to using friction shifters very quickly. I actually quite like them now even for commuting.