I've never compared the sears and hammer hooks of both, no idea if they'd interchange. Frankly I doubt it. A try of the 52 hammer might be interesting.

Light stoning of the sear surface that mates with the hammer will help. As will adjustment of the tension of the sear spring. That's the flat spring in the frame. A spring kit with a reduced power mainspring and polishing of the inside of the mainspring cup will help.

Factory spec for the SA pull on the S&W service autos is 4.5 lbs minimum. I personally wouldn't drop below factory specs. I find too much a difference between DA and SA pulls to screw up my transitions between the two modes. Allthough that doesn't seem to be your usage..