There is only one notable change from '78 to the 2005 era on all models including the 44 BH 50th model also on hammer base size. The 44 50th BH hammer base will need to be trimmed flush to fit the '78 grip frame ears. For a lot less work, I'd suggest trading your '78 grip frame for the same size but made after 1997.
INTERCHAGEABILITY OF GRIP FRAMES
Chapter 1. Grip Frame Ear Height Change to be aware of: the ear height around the base of the hammer varies on all grip frame ears slightly due to hand fitting at the factory, but there was one specific big height increase. To simplify production in 1997, Ruger increased the height 1/16" on the standard cylinder frame mating surfaces on both sides of the hammer to match the Bisley model frame ears so any style grip frame could be assembled to any main frame. Therefore the ears on all the other standard plow handle grip frames after 1997 had to be made ~ 1/16" taller as well. So there's basically two sizes of the STANDARD plow handle grip frames: as short as .530" pre 1997 and as tall as .590" after 1997 (for example: Original Vaqueros above serial range 56-XXXXX). Measure from the very top edge of the grip panel to the top of the ears. That's why standard grip frame swaps are simplified if any acquired grip frame matches the vintage of your Ruger that you want to put it on. This also affects the standard hammer base fit to the grip frame ears on plow handle grip frames, except new hammers designed after 1997, like the New Vaquero and New model flat top Blackhawks.
The grip frame 'ears':
Ears & Hammer Base sizes: Ruger has only enlarged the hammer base to match the taller grip frame ears on the newly designed hammers introduced since 2005 such as the New Vaq standard 'long horn' and Montado hammers, the NM Flat Top Blackhawk hammers. All other hammers designed prior to 2005 used on current model and Old Model guns are small base and do not match the post 1997 tall eared grip frames. Some people don't mind. If I install a small base hammer in a post 1997 gun, I fit the grip frame ears to the hammer. I also have to do this every time I install post 1997 grip frames such as the N Vaq and Flat Top XR3 size steel grip frames or XRE-RED size steel grip frames on pre 1997 New Models, or on Old Model Rugers.
Poor hammer to ears fit:
Mike Campbell photo.
Montado hammer base flush fit to ears:
The top small base hammers 1.071" – 1.076" (measured in line with the two outside holes) predates the c. 2005 large base newly introduced model hammer designs. Measured on the centerline of the two large holes from back of hammer base to over the full cock notch.
Bottom hammer is a new Flat Top Blackhawk with large base 1.122" – 1.130" and narrow shank.
Mike Campbell photo.
Another detail: Narrower shank hammers (except Montado hammers) coincide with the larger base hammer design on the New Vaqs and the 1st anniversary new mid-size in 2005 flat tops and 2006 and later large frame flat tops, and in my opinion are much better looking. I know of no other reason for it other than the improved looks. For many years I was relieving the shanks by hand.
Right hand hammer is after c. 2005 up to current production with large base 1.122" – 1.130" and narrow shank.
Mike Campbell photo.
Above photos from here:
http://www.rugerforum.com/phpBB3/viewtopic.php?f=3&t=213730&p=2136804#p2136804
I hope this is of additional help,
