The one owner I know had his Lycoming 0-360 ported and polished when it
was rebuilt and it was a disappointment. If anything the engine
performed worse after the rebuild. I know it is a data point of 1 and
might be due to other factors, but that is what he experienced. My take
is Lycoming ports and polishes pretty good. It might be possible to
improve it, but I've never seen the evidence. It's a pretty inexpensive
procedure to change it as they port and polish anyway, and if there
were a better way to get more flow, Lycoming would do it. Porting is a
bit of a black art, sometimes it works and sometimes it doesn't, air
flow being the random thing it is. Lot of people try, it is fun to look
at those compound curves and nice polished surfaces and think you might
be able to improve it or enhance it. I certainly wouldn't pay any more
for a custom port job, and I'm not sure there are any STC's for it
anyway, which supposedly you would need as it is a change in the engine
configuration.

He stated he would not do it again.

Sorry I can't be more hopeful.