I think but am not 100% sure that the W53 head was fitted to the later L18s, ie the 810 180Bs not the 610 180Bs which had the A87 head. The U67 is the standard L20B head and is open chamber and hence low comp.
An A87 head on an L20B block gives good compression, probably a little bit more than you mentioned you were after. W53 is probably a similar story. I will have a look in the Honsowetz book to see what it says about the W53. rob240z from the NZ site reconditioned the SSS L18 in his 180B SSS P810 and that has a W53 so I will ask him for you. I think they are a peanut chamber head with the same size valves as the A87 and U67.