"What is involved with that process exactly ?"
Get TKM or Pinnacle to ream the cylinder for 9mm, cut it for moonclips, and thin the extractor star to match the moonclips. When you get the cylinder back, time the chambers to match the gun. On average, it takes me about 5 minutes per chamber to do that. I do it while watching TV :-)
"Where did you source the cylinders?"
Titanium .38Sp/.357Mag cylinders from Midway. I got six. I think they are out of stock at the moment.
"I'm know the bore diameter is close enough for a 9mm conversion - but what sort of accuracy have you noticed ?"
No change in accuracy.
"I thought there could potentially be down sort of "tolerance stacking" effect".
Doesn't seem to be.
" I think a light 9mm jframe would be slick !"
12.5 oz with the titanium cylinders and Altamont combat grips.
A little heavier with Hogue laser grip.
I use 9mm 147 gr JHP
Recoil is more brisk than .38Sp, but not bad.
I don't plan to try .357 Mag in them.