I wouldn't worry about it. They would have had to do the grinding away from the engine (and cleaned the debris off before refitting.) The shims are available in thickness increments from about 2.8mm I think (very thin) to 4.7mm (very thick). Yours are probably in the middle of the range as I've yet to see a standard engine with the valves anywhere near the ends of the scale. In fact, they seem to leave the factory with most shims the exact same size!
So, by grinding some material off, they will just have moved the shim a few steps down the thickness range - there will be no impact on the other parts "in there".
In fact, the adjustment they made may not have been strictly necessary. Standard specified clearance for the older FIAT SOHC engines (e.g. 128) was 0.30mm, rising to 0.45mm-0.55mm over the years presumably to make assembly/adjustment less precise. I'm told this was made possible also by revised cam lobe shaping - 'quietening ramps' reduce the sharpness of the valve lift to take up the clearance more quietly. My 128 engine ran a performance reground cam with tightened clearances of 0.15mm (I think they specified a small clearance because there were no 'quietening ramps' in the reground profile.) The purpose of the clearance is to allow for valve expansion with heating and ensure that always some clearance remains. Since my 128 engine was 'high performance', and 0.15mm was enough, I'm now a little blase about adjusting clearances if they're a wee bit too tight. But that's just my opinion, mind
Now as for your other, fuel system issues, I'm sorry that I have nothing more to contribute as I have no diesel experience (and I don't think we have many members that have a diesel Uno?) If it was mine, I would fit some proper new hose clips on the connections you have identified, then just keep using it and checking the coolant level. I reckon you'd notice the level going down if you had a head gasket problem.
-Alex
