For your car maybe keep this one stock
ALTHOUGH YOU DID NOT ASK I will be obnoxious and give my $0.02. Most of us will give the same recommendation to get it solid and reliable with good quality parts, clean it up and have fun with it. I don't know your skillset or expertise but more than likely If you do an engine swap you will be married to it and always tinkering and your dad pissed the thing is always down for the count with some goofy issue. If you do any tuning you know what I mean. Another point is even though you may be very crafty and have access to tools etc it is always far more expensive than you think to reengineer a car and always takes much longer than expected. Where do you stop? Engine with trans adapter, Engine and gearbox as a power pack, cutting up the chassis and then reinforcing it? It is a big job for sure.
Even a stock restoration will take longer than you think. I will jump to the conclusion you have not done a full on resto yet but I could be wrong. Just look at restoring the front suspension alone, by the time you assess what you need, what you will repair and what you will replace you are a week to a couple weeks into a tear down - yes it takes that long especially if this is your first time through a new car. Then you find the parts you want and purchase them - add another week or two. If you decide to media blast parts and get them replated or coated now add on another 2-3 weeks ( will be concurrent with new part timing). Now you get the bits all together and reassemble everything. Give that a few days to a week. So just restoring the front suspension you are somewhere 4.5-7 weeks into it depending on how aggressive you are. Some bits will come right apart and some won't no matter what car you have, that is not just Fiat related. Now take that summary and go through each system, rear suspension, engine, cooling, electrical, interior etc.
Don't know your dads preference but most of the guys that tune the hell out of these end up detuning the car or ditching it for a more stock one as they get older. Most will tell you that in its stock, purist form it is the most fun. I have had both ends of the spectrum with the X1/9s and my tuned car is a blast for about a half hour then it is ready to put away. My old stock 74 I could just jump in it take off cruise anywhere without complications. It was a fun car. The engines are reliable if you use good parts and do a very mild tune. Honestly how many miles is he really going to put on it a year as well - just volunteering that before you go down the path of "this thing has to be bomb proof for ever".
Assuming by your tag you know the 4AGE, definitely not a bad engine but my $0.02 again is to save that one for yourself in the MR2, Corolla or get totally nutty and build up a mid engined tercel.
