Wheel cylinders for 11 inch brakes

I'm cobbling together the parts I need for drum brakes on my 8 3/4 axle. Already bought a pair of 11 x 2.5 finned drums through rockauto and now looking for wheel cylinders.

I see on Rich Ehrenberg's Ebay store that he's selling pairs of 10-11 inch drum brake wheel cylinders for nearly $40, says they are "improved design" over OEM to accommodate front discs. Here's what he says on the ebay add:

Here's an oft-needed item: a pair (that's two [2] pieces) of new, improved-design replacement rear wheel cylinders for all muscle-era Mopars (1965-74) equipped with 10 or 11" rear drum brakes.

Why you need them: Stock Mopar rear wheel cylinders of the era contained basically 'one way' internal seals. Air was prevented from entering the system, on the return stroke, by means of a residual pressure valve located in the master cylinder. But modern master cylinders, as used for most front-disc swaps, do not have these valves. So, if you make the usual disc swap with OEM wheel cylinders in the rear, the result will be an eternally spongy pedal! Do the job right with these beauties, built by an OEM Chrysler supplier, specifically designed to alleviate this nasty condition.

I suspect this wheel cylinder is available for much less than what they are being sold for on Ebay...rockauto has Raybestos and other rear drum wheel cylinders for around $5 - $7 each.

Does anyone know who makes the wheel cylinders referred to in Ehrenberg's Ebay add, and the part number?

Cheers