I see no reason whatsoever one cannot swap out a Ti cylinder for a steel one. Brownells used to have them for around $75. I wanted to buy a 638 put in a Ti cylinder and remove the lock. But and here's the BIG but. the cylinders available are chambered for .357 not .38. The thought of accidentially putting a .357 in a revolver not originally rated for it (al la a 638) scares the snot out of me-so I put that idea on the back burner. Plus I already have a 337.
Maybe I'll buy a 638 and put my 337 cylinder in that.............-naw got too much other stuff to buy.