The 327NG comes with a black SS cylinder, not a problem to machine. Ti, like that 327PD's cylinder, is tougher to machine than SS - and galls easily. Choose your machinist carefully. I'd call S&W - 800-331-0852 - and ask them what they'd charge. Of course, a vestige of the original cylinder's back is left on the outer circumference to support/headspace the ammo. Also, the inner edge of the extractor star should be 'eased' to assist reloading.
If you like the 8-slot moonclips that came with your S$W X27, consider ordering more from the manufacturer - Ranch Products. They are $50/50 or $75/100 delivered, in blued steel. Starline brass loads easily - Remi's are nearly as easy. Not everything will even 'fit'. The Remi R38S12 .38 Spcl +P 158gr LHPSWC load fits and reloads faster than the .357 Magnums. Of course, if you've been spoiled by a 25/625 in .45 ACP, like my 625JM and .45 ACP ball ammo - which loads as if it was on a tractor beam, the spindly spider legs are aggravating - as someone suggested, like trying to push wet rope - and take some time. For 'carry', you definitely need a protective sleeve - stiff leather at a minimum.
BTW, I have had a 5" JM PC627 V-Comp for some years - added a 4" 627 Pro 5/08. That 4" 627 Pro is the 'keeper' of the pair. I keep four food containers loaded with 14 loaded moonclips, 125gr JHP poppers in .357 Magnum cases, each for range use - and have a few moonclips with those +P Remingtons loaded for emergency 'home' use. Fewer .38s fit the clips easily than the .357 Magnums. I use the long Brownells nutdriver-style de-mooner - it'll hold eight empty .357Ms inside - fast de-mooner. At ~$15, it wasn't much - and looks better than a hunk of pipe in your range bag.
Stainz