My first car was a 1961 1200 Cabriolet that I owned from 1973 til 2003. Here are some things I know:
Find a 1200 cc block from a 1100D that has a spin-on oil filter on the lower left side of the motor if you can. You get 1223 cc over the 1089 of the 1100.
The generator brackets ALWAYS break and you will see countless ways to try and prevent it.
The cylinder heads crack between 2 and 3... without fail. You can have heads welded and shaved about three times before you break into the water jackets.
Find an intake from the 1100R. It will convert you to a sidedraft carb. The Weber 32 DCOF (not to be confused with a DCOE) or Solex are nice little carbs and you can mod the manifold for a DCOE pretty easily.
The 1100R exhaust cast exhaust manifold and tubular head pipe will yield one or two more HP than the stock 1100/1200 set up.
Valve rockers get an indent from the tops of the valves but these can be resurfaced by a machine shop.
DO NOT let anyone tell you that you can resurface the cam followers. The hardened layer is so thin that they will be ruined by resurfacing. They will have small pits on the surface but they will work okay.
The timing chains are notoriously noisy on these motors and there is no chain tensioner. Get used to the noise.
Someone used to make 4-ring pistons for these motors that had an extra oil ring below the wrist pin. That helps tremendously with piston slap and top ring breakage (which happens when you are young and think every motor should rev to 7000 rpm).
Valve springs tend to be weak. Replace if possible.
For the rest of the car, if you have an old one, Fiat used to put right hand threads on the right hand wheel studs and left hand threads on the left side. This is easily converted by changing drums. If you can find a set of station wagon rear drums, they have nice cooling fins and are very much more attractive than the plain ones. Front brakes can be converted to disc from the 1100R or an 850. You need the rotors, calipers, dust shields, and caliper holders (whatever they are called). You have to make a new mounting bracket for the brake hose to hardline connection. But, I did this at age 17, so it can't be too hard. I did not use any kind of proportioning valve or change from the single chamber master cylinder and the set up worked fine.
Transmissions are pretty solid, but watch crunching into first gear (non-synchro), and if ever the tranny starts jumping out of a gear (3rd is one that can cause problems), you need a new sliding gear and synchros. There is no other fix (having gone through a transmission 13 times in one summer trying to fix that problem).
Books are still available for these cars, check on Alibris or other online bookstore and you will find manuals that can help.
Steve