A couple of thoughts on work benches and vises:
The workbench is a very personal thing that is based on the type of work, space available, physical stature (ht) of individual, and numerous other characteristics that make it difficult to provide a perfect answer to the OP. I would say that broadly, if the only singular use for the bench is the building of a Kibler longrifle, the bench requirements can be fairly spartan and a small, narrow bench will suffice. Even a prebuilt, purchase wood working table may be good (search Sjoberg bench:
https://sjobergs.se/en/product/sjobergs-nordic-1450-storage-module-0042-35011/).
With respect to the vise, two thoughts come to mind. First, don't forget the other end of the long rifle needs to be supported in some way at the opposite end from the vise. The PA longrifle stocks are long, thin and fragile. Even vigorous sanding can be risky if not properly supported. This may require some sort of outrigger opposite the vise.
The vise itself can be of many configurations. When I started building, I fit homemade wooden jaws between the jaws of a Columbian machinist vise (C44). It worked fine for years. Then I decided I needed a pattern maker vise, and found the parrot model to be within my price range.
What I found is that the parrot style uses the same torque to control the swivel mechanism as to tighten the jaws. That is to say, if you want a tight, nonswivelling vise, you must add more torque to the jaws via the main screw. This has always made me nervous especially when clamping the fragile lock mortise area. But, they are handy and can easily adjust to nonparallel faces.
Parrot type vise:
https://www.amazon.com/HFS-Parrot-V...efd16e931dd6fc2cf697c35&qid=1733095838&sr=8-3
Pattern maker vise:
https://www.amazon.com/WoodRiver-Pa...fd16e931dd6fc2cf697c35&qid=1733095838&sr=8-11
So I am thinking the true pattern maker vise is probably better, but way more expensive.
I hope this is helpful. I am including some pictures of my traditional woodworking bench which I use for my builds, but is likely over kill for most needs. Picture three is an example of an outrigger for supporting long workpieces.
Cheers, Rick.