IF you don't have 'em, get 3 120 grit flapper wheels for your rotary tool.... I got by with 2 on 96BonnevilleL67'* M90, but on the 99 M90 housing I did for my dad (giving it to him for Christmas to put on his 02 Park Avenue Ultra) I needed 3, plus about ten 120 grit sandpaper wheels, a Dremel 9905 (?) carbide bit, 1 sheet of 600 grit and 1200 grit sand paper for the finishing. Still had a hell of a time getting the edges of the inlet that are really tight, but managed to smooth about 75% of the roughness out.
Good luck with the rest of the process.....
P.*. Looks like you have a better camera than me... I've tried taking about 50 pics of my porting, but close-ups make me wonder what I was taking a picture of.
I might do a little more, but i got about 90-95% of the roughness out
i didnt have to use all the Bits you had to Marty,
i only used
1 80grit flaper (50% life left)
1 120grit flaper (still lots of life left)
2 80grit drum wheels (killed them both)
and some polishing stone wheels (went throught the different abrasivnesses, last one was so smoth it felt like rubber)