Best option to find an original pre war K-frame hammer and trigger together may alleviate some fitting issues but I am pretty sure some fitting will be required to make anything work. The more parts you have that are already fitted to each other will be better. Most likely a .38 M&P 1905 4th change-parts will be easiest to find as many were made but somebody with gunsmithing skills is a must once parts are obtained. Good luck, keep is posted.