Sorry about you sight issue. A replacement standard hammer for the vintage should be a relatively easy swap. Probably Numerich as a source. There are aftermarket hammer spurs or hammer extensions, but be aware of the hammer width, I want to say the pre-cross bolt safety hammers are narrower than ones for the cross-bolt safety rifles. Uncle Mike's makes one for both style hammers but it is rounded. Try giving Jack First Gunshop a call for an older Marlin hammer extension. They also show up on ebay occasionally, but can get pricey.
I shoot right handed and like my extensions out to the right. So I understand your desire to switch. All of the ones I have seen are reversible and are secured with an Allen head set setcrew.
Here's a shot of a rounded one that came on my used 39A (1979 year) when I got it.
Here's a shot of the flat style on my 1894C, I have since put the same style on my 336 and 39A, attached extended to the right
How do you like the peep sight? Is it a Skinner, XS...I have seen that type but cannot remember which it is. I would like to get a ghost or peep but am not sure it will be usable for me. How well does it work out to about 100-150 yds?