There are actually quite a few more than 300 of that model.
When those first started popping up it was an uncataloged model of BNV-474. Ruger also did a few KBNV-474's back then.
They were produced because they were leftovers from 4-5/8"" .44-40 production, so Ruger used them up as 4-5/8"" .44's.
Well, both models started showing up out of nowhere and were bringing up to $1K by collectors when they could find them.
It got to the point were several people were asking their distributor to watch for them if any came in. Distributors got the hint and started ordering the model through Ruger...and at that point Ruger decided it was maybe a good model to produce. So after that they made thousands in the large size Vaquero frame in blue and stainless. There were also a few of each with simulated ivory panels although those are quite a bit scarcer.
And, Ruger also made some Bisley's in blue and stainless 4-5/8"".
No Bisleys with that barrel length are known to have been produced with simulated ivory.