Re: Head performance modification.
Rick's right, the whole "lumpy idle" thing is a throwback to the 60's and 70's when people used to throw a full race cam in their mini then wonder where the idle went.
Cam design has come a long way since and it's quite possible to get decent gains without the old compromise of losing the bottom end completely.
The Alfa Nord engine has bags of low end power anyway so you could afford to lose a bit if need be.
As for the TS conversion, I don't see how it'd be cheaper than a Nord rebuild. Assuming that you'd rebuild the TS anyway, all the gaskets, pistons/liners and bearing wills cost you about the same and you have to add the cost (say £200) of a scrap 75. You wouldn't really just throw an engine from a banger in without rebuilding it would you?
OK, so you end up with 150 bhp not 130 so it would be cheaper overall if that was your end goal but if you just want a rebuilt engine you're probably better rebuilding the one you already own.
A head skim on your engine is worth it, I got the wife's Punto one done for £25 cash so it's practically free horsepower, even if only a couple.
Alfa 75 TS LE Veloce
Fiat 125 Abnormale