Apologies up front
 

I apologize ahead of time if this question is a repeat (I searched to no avail) or offends vintage collectors. I have a really nice 1970 Bridgestone Grand Velo with Campy Record components. I ride over a lot of hills and would like to change the gearing, but it seems I am really limited in what I can do with the existing drivetrain. I was wondering if I could put a compact crankset on this or, if this is not possible, replace the entire drivetrain with a modern one. I'm not interested in keeping the bike authentic. It is the best riding frame I've ever been on and I want to ride it!

Find a nice Sugino AT crank to put on there, maybe need to change the front and rear deraillers to handle the triple, and go!

You could probably put a whole new drive train on it, but I just "upgraded" my Nuovo Record bike to a triple with a long cage rear derailler. Triplizer inner rings and spindle from Bicycle Classics, rear "Rally" deraillers can be found on ebay. If it doesn't rain this weekend I'll be able to try it out.

Could probably find good Japanese substitutes on ebay too.

I am not sure of your BB size/threading, but I believe it is standard English threading and width, if so, it is easy, if you are not locked into Campy...

You can find vintage cranks with 110 mm BCD, and run a compact chain ring setup if you want. You would need to probably switch BB and crank, and lower and adjust your FD, but otherwise you should be fine. Some Sugino and other cranks from back in the day used the 110 mm BCD.

You can also switch to a modern BB/crank while retaining the rest of the drivetrain if you want as well. Stick with an 8 or 9 speed compact crank/BB to keep it affordable and compatible.

I personally think the right vintage crank would look best on the bike, while accomplishing what you want.

As others above have mentioned, there are triple crank options as well.

MTB rear derailleur and cassette would be a lot cheaper than crank options.

I've got a nice Sugino AT triple, send me a PM if you are interested.

I replaced the rear wheel on my bike with a 9 speed cassette system, 9 speed chain, and appropriate rear derailleur. Had to spread the dropouts. I had some questions about the chainrings, but they seem to work fine.