My comments were based on the presence of .38 Special ammunition with the gun. Of course, it might not fit the gun at all, but I was pointing out that some of those revolvers came from the factory made for .38 Special and that IMHO it would be safe to fire standard .38 Special loads in such a gun.
Since I have never seen the OP's gun, I did not carry out extensive metallurgical tests of the steel in the cylinder or the frame. But the standard .38 Special is not exactly on the cutting edge of high pressure technology, though it might be too much for extensive shooting in guns not intended for it.
As for cylinder diameter, it is not the sole and only determinant of strength in a revolver, but it is a useful one. The specifications for the Colt cylinder simply say "medium steel" with no heat treatment.
Colt barrel markings remained the same throughout production, "COLT D.A. .38". The only way to tell if bored through cylinders are factory is by the serial number or military model number.