I think I said this before in one of the "Wolfhound / Skiff Switched" threads, but there's just no way to be completely faithful to the historical stats, and still balanced for gameplay. As you say, the Apollo SPS engine was relatively low ISP due to hypergolic fuel and so forth, but thay was based on the need to store fuel in space and easily restart. The J-2 had much better efficiency, but that came with all the disadvantages of hydrogen (low fuel density, poor storage) etc.
I think the Wolfhound as a monopropellant engine with Isp of, say, 320 s and thrust matching the Poodle would still be a better representation of the historic engine. At the same time, the Skiff certainly still looks too light and too weak for its size. Maybe its place is between the Skipper and the Mainsail (which puts the thrust near the Vector, but the Vector has its niche for the small size and good atmospheric Isp, and the Skiff ASL Isp may be nerfed to, say, 220 s to emphasize its intended use).
Tuning changes in 1.6
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I think the Wolfhound as a monopropellant engine with Isp of, say, 320 s and thrust matching the Poodle would still be a better representation of the historic engine. At the same time, the Skiff certainly still looks too light and too weak for its size. Maybe its place is between the Skipper and the Mainsail (which puts the thrust near the Vector, but the Vector has its niche for the small size and good atmospheric Isp, and the Skiff ASL Isp may be nerfed to, say, 220 s to emphasize its intended use).