The only 'misfire' I ever got with the original 2 carb engines of the 70s and 80s was at the change over from idle jets to main jets which is much lower than 3500-4500 rpm even on a car with emission control carburetors......
Under what circumstances does the engine misfire......
As for the head gasket going. Hopefully you are 'retentioning' the head on a regular basis......ie every 6 months....Then their is the regular adjustment of the timing chain ......etc etc etc....
The Alfa Romeo Owners Bible by Pat Braden will be a good read.....and maybe his other book ...
NB I had a new 1983 Alfetta GTV 2.0 for 19 years and over 60,000 miles with the engine never opened (from new).....
Amazon.co.uk: Alfa Romeo Owner's Bible 1954 on (Owner's Bibles): Pat Braden: Books
Amazon.co.uk: Alfa Romeo All-Alloy Twin Cam Companion: 1954-1994: Pat Braden: Books