Different cycle efficiency.

[Storm_Eagle]

Hi. From what i have read in the end of the period where Stirlings where considered for cars and busses in the 60's and 70's with the Philips / GM motors the double acting swash plate type was the only one being seriously considered. Mainly because of power density and cheap production because of fewer parts i think. But from what i can see this is basically a alpha type configuration, and from other sources i have read that the alpha type is the least efficient of the three main types. What sort of efficiency did they get from these double acting swash plate style motors?