The original #5 was NOT a 44Mag. 44Special, I *think*. The primary frame was basically a Colt SAA which is a bit smaller than a Ruger and not able to handle 44Mag pressures.
The Ruger "Bisley" grip frame is clearly influenced by the #5. The shape is dang near identical, but the Ruger version is a bit bigger, esp. longer.
By switching over to the thinner "Gunfighter" pattern grip frames by Eagle and others, you can probably make the Ruger Bisley feel a LOT like the #5. But at a price: the Ruger Bisley grip's recoil control will be compromized by thinner grips, to at least some degree (depending on your hand size).
Now let's take another look at this: when Elmer Keith was doing ballistics research in the 1920s and 1930s, 45LC brass was just crappy. It was the old "balloon head" pattern. That's why he switched to hot-rodding the 44Special and then took that out to Magnum size by influencing S&W.
But he *started* with the 45LC. Had the brass in that caliber been as good as the 44 brass, he'd have stuck with it and influenced S&W to "magnumize" THAT - we'd have had something akin to the 454Casull (at a bit less power) in the 1950s. That's the route Dick Casull eventually took once 45LC brass of modern construction became available.
Now throw in another factor: the Ruger Bisley is bigger and weighs more than the original #5. By switching to the 45 bore, you cut the weight of the Ruger just a hair, to try and duplicate the "muzzle point feel".
So that's what I'd do to "recreate the #5": Bisley Vaquero in 45LC, appropriate barrel length (5.5"? I can't recall offhand), #5-type base pin by Belt Mountain, Eagle Gunfighter grips (smooth, not checkered) and then start in on the sights. Keith used a gold bead front and small horizontal lines down the front of the sight as "elevation markers" for long-range shooting.