Retrofitting a modern drivetrain on an old bike, caveats?
 

I have this bike in a size that doesn't fit me: http://bianchiusa.com/05_bergamo.html That's a 7-speed cassette, a 3-speed hub, and a single chainring in the front.

And a 1983 Ross Grand Touring 12-speed. It's your standard 80s road bike with drop bars, downtube shifters, and mostly Altus components.

I would like to take drivetrain components (Wheels w/ internally geared hub, Crankset, Chain, Derailleur, shifters, and cabling), off the Bianchi and retrofit them onto the Ross.

I am not an experienced mechanic and would like to know what problems I'll run into ahead of time. I have read a little about derailleur adjustment and limit screws but have never actually done it.

I know that I will need to have the shop do the crankset work for me, as I don't have the tools. And I am going to have to get a HubBub adapter to run that grip shifter on the drop bars (Unless there is another way??).

Is there anything else that I need to look out for?

Also, bonus question: Would it be possible to leave the double chainrings on the Ross and run this as a 42-speed bike? Mostly just a silly academic question.

Is the spacing across the rear hub the same as the spacing across the frame? This has changed over the years and will be critical to the conversion.

An excuse to build a wheel ;)
On eBay I saw 126mm spaced rear hubs. Intuitively that seems like it could be pursuaded into either 130mm or 120mm spaced rear drop outs.

I suspect that the 83 Ross frame is 126mm between the dropouts and the SRAM Dualdrive hub from the Bianchi is a 135mm device. This could be a stretch without cold setting the frame. Read Sheldon Browns Frame spacing article.