I`ve done my Twin Spark -in my 2 litre 156 with pleasing results on the road however I am extremely experienced having owned a Euro workshop here in NZ and built many a performance engine. I had a flow bench then so picked up what and what not to do which applied generally. I simply "cleaned up the ports " with lots of time spent on the throat area just behind the valve and the top of the port around the valve guide. That and simple port matching, including within the intake tubing plus exhaust manifold to head matching. I can now hear an induction noise just like my carbed 105`s and 101 Alfas. It is definitely more lively and revs faster.
I wouldn`t recommend doing it though if you have no experience as you can always go the opposite way and lessen performance. Bigger is definitely not better. Take it to a experienced professional.
Just for your information:
There is a well-reputed company named "NG Motorsports" located in Germany.
They are specialized in cylinder heads. They use CNC for porting and also have a CNC-program for the Twin Spark ready available.
Using CNC you get reproducible results.They offer a lot of options like larger Valves from Supertech, tapered bronze valve guides, multi angle valve seats, special surfaces, ...
They are featured in a lot of tuning-videos on YouTube, but mostly in german language and not for Alfa Romeo. For example "Philipp Kaess" did a great series with them.