Why in your opinion would Whit B work better over 1968? Also, what pitch rate, oxygenation and temperatures do you prefer?
Whitbread "B" just works with this recipe. The different ester profile combined with a higher attentuation level than Wy1968 seems to enhance the malt and hops in this recipe while keeping the overall flavor profile distinctly British. If I were to recommend a different strain for the recipe, it would be well-aerated Ringwood (Ringwood has high O2 demands).
As far as pitch rate goes, like most British brewers, I tend to underpitch my British-style beers. Basically, take the cell count that Mr. Malty gives you and reduce it by a third to one-half. British ale is not supposed to be ester free. If you decide to underpitch, you need to ensure that you are not pitching stressed yeast cells and your wort is well aerated; otherwise, you risk having the culture throw a ton of trash.
I ferment all of my British-style ales in the 65F to 70F range (sometimes they creep up as far as 72F) without attemperation. My basement remains below 70F most of the year.
With that said, please feel free to use whatever you have on hand and what pitch rate makes you happy. That's beauty of making beer at home.