I know this one is a couple weeks cold, but I thought I might share the outcome of this thread - I FINALLY got these finished up, and while my photography skills are lacking, I thought I'd share another illustration of the end result when converting a Ruger Bisley Hammer to work with their plowshare or birdshead grips.
The 3 Bisley hammers pictured in the middle of the pack below all started out looking exactly like the center bisley - a standard Ruger product with a LOT of junk in the trunk. Before you take on this project for your own revolver, you need to recognize which model you own, such you can modify the hammer appropriately to match your particular grip frame. The age of your revolver matters, in this case.
@farm23 has a pre-1998 Blackhawk, so the "rump" of a standard Vaquero/Blackhawk or Super Blackhawk hammer would match the void between the upper bosses of the grip frame, so making a Bisley hammer fit one of the Pre-1998 Blackhawk's is just a matter of matching a Vaquero/Blackhawk or Super Blackhawk hammer. In the photo below, you'll note the 3rd hammer from the left is a Bisley spur, but with NO junk in the trunk, similar to the Super Blackhawk and Vaquero/Blackhawk hammers to its left. If I had cut his hammer to match the two hammers at the right, it would not fit in his grip frame, as the bosses on the Pre-1998 grip frames were slightly smaller, so a New Vaquero or Montado sized hammer won't fit (aka, the tracing in the photo I posted above).
@dickydalton, alternatively, has a New Vaquero, which has the same grip frame profile as the Post-1998 Blackhawk, Birdshead, Super Blackhawk, and Vaqueros, however, unlike the hammers for these other models, the New Vaquero hammer has more junk in the trunk, such that it fills in void between the upper bosses of the grip frame as well. These other models would have a small void between the bosses, where their standard hammers (the same profile as Farm23's grip frame) would be slightly smaller than the grip frame bosses. Since dickydalton has a smooth profile New Vaquero hammer, I cut this one to match a New Vaquero hammer, such it matches profile to any Post-1998 Blackhawk, Super Blackhawk, Vaquero, or New Vaquero grip frame. Note his hammer, 2nd from the right, has a small bump on its rump, which matches the profile of the New Vaquero hammer at the right. Farm23's hammer would fit in dickydalton's revolver, but would leave a ~1/8" void sunk between the bosses of the grip frame - which would match a conventional Post-1998 Blackhawk, Super Blackhawk, Vaquero look, but definitely isn't as attractive. The reverse, again, isn't true, as dickydalton's hammer would NOT fit into Farm23's Pre-1998 Blackhawk.
When installed, both of these will match their respective revolver's grip frame bosses, giving a cleaner look than many of the standard Ruger plowshare grip revolvers.
L to R: Super Blackhawk, Vaquero/Blackhawk, Pre-1998 Modified Bisley (Farm23, Standard Bisley, Post-1998 Modified Bisley (dickydalton), New Vaquero.