9mm Cylinder numbering question

[rmc25]

I got the 9mm bug and so I decided to go through some parts boxes today. I found two Ruger 9mm cylinders. One has 3 digits and the other one 4.

Three digit is faint and hard to read. Could be 988 but don't trust old eyes.

Four digit is sharper. Picture attached.

When did Ruger start the 357/9mm convertible models?

 

[rugerguy]

Do not think that is actually a "'fourth" digit, often see an extra symbol?? letter?? or some weird "scratch" often on the opposite ( few spaces,chambers over) just had one recently it was an "X"??? was told once it was the fitter who did this?? I believe the start of convertibles ( an "X" would be in the catalog number of any factory letter) was in 1967, nothing marked on the box itself but on any cardboard shipper ( wrapper)

 

[bykerhd]

Check the measurements front to back against the stock .357 cylinder.
If you have one with the same measurements, it may work, if it times ok.
You would need to invest in or borrow a range rod to check alignment.
If the range rod confirms alignment on each chamber is ok I would consider that good.
BUT, I am no gunsmith.