A 4516 top end with a dual-recoil spring sounds like it's a -1 variant or later (*edit* - I'm completely wrong about that). IIRC the no-dash models had a lighter slide and a few other differences that could be problematic.

If the gun functions fine then the only real concern is if the decock timing is within spec with the 4516 top end on it. A quick check involves cocking the hammer, then placing a 5/64" drill bit end in the channel under the left-hand decock lever and attempting to decock it. It should not decock with this bit in place.

If it does, then the foot of the sear release lever needs to be adjusted with a file/diamond stone, keeping the same angle as the original, until the gun does not decock with that bit in place. This can be tedious and involves a lot of dissasembly/reassembly of the small pistol parts.

The second check would be to then place a .045" bit (3/64" is close) in the channel and make sure that the gun does decock with that bit in place. If not, then the lever has been over-filed and you'll need to start on a new one.