My old 10SI has both of the mounting holes on the front of the case so reclocking would not affect the mounting at all, only the position of the terminals. This is also the case on my new CS144, but may not be for others I don't know.
The 10SI and 12SI were used in the 70s to late 80s. I don't know the exact yearts. The 12SI had a larger case and usually had a higher output.
The CS105 and CS144 were used from the late 80s until at least '99. Again, I don't know the exact years. These alternators generally have higher ouput, especially at low RPMs, than the earlier SI alternators. The CS144 has a larger case and commonly came in 124 amp and 140 amp versions.
I tried to clock mine without pulling it completely apart, but I must have pulled a little too hard. I took it to Checker and had it tested after I clocked it and it got a clean bill of health. I told the parts guy that it came out of '97 1 ton chevy with a 454 so he could figure out how to test it.