S&WMod65fan,
To directly answer your question, no, the parts are not available to update the 638 to 638-1. The changes were yoke retention system and radiius stud package. The yoke retention would require replacement of the yoke, re-drilling and tapping the frame for the new yoke screw, and re-drilling the side plate. The radiius stud package requires replacement of the hammer, trigger and cylinder stop studs which are staked into the frame, a factory job if the would even do it. This would also require replacement of the hammer, trigger and, probably, cylinder stop to match up with the radiiused studs.
By the time you paid for all the parts and labor to change this gun you could have bought a new model and saved a lot of time.
I would ask if, in the one circumstance you had problems with the 638 in question, did you make any measurements, or just listen to "someone" who thought it could have been caused by heating? With the dimensions involved and the possible temperatures from firing, it is unlikely the extractor rod could have lengthened even 1/2 of one thousandth of an inch, a fraction of the thickness of tissue paper. Do you really think this was a reasonable explanation? As you can see, even if you could have up-dated the gun to -1 standards there is nothing which would have addressed this issue. I am not saying you didn't have a problem, just questioning the conclusion which was reached.
