Being this appears to be essentially resolved, I have a similar/related question. I have a Model 64-5 that I purchased with the NY hammer (dao). I purchased a used K frame hammer (with spur and single action notch) off of eBay that looks like it is hard chrome plated. My original hammer had the nose spring, but the replacement did not. From the above posts, it appears that is of no consequence. Should I just install it (the hammer) or removed the hammer nose rivet, make the spring notch and install a spring and new rivet?

Thanks for the kind help!