My .02 for what its worth....
The Olympus housing for the PL-2 can't be beat for the price and very well made. Ignore the 40m depth limit (assuming your training allows).. that's lawyer crap... I've had mine to 160' many times with nary a leak and the buttons, albeit stiff, still work well. IMHO, no better bargain exists in underwater photography today. For just under $3k you can have a PL-2, lens, housing, dome, and twin strobes. That's LESS than the price of a dSLR housing ALONE (no camera, ports, or lenses).... Zen makes a flat port for the 45mm macro and domes for the
7-14 and 9-18, both which are also compatible with the 14-42 kit lens. All Zen products are also very reasonably priced and optical glass -- don't want to argue about whether that's better than plastic... just saying....
IMHO, the only thing those other housings have over Olympus is the electrical connections for the strobe.....if that's important to you. Optically-fired DS-TTL and manual work just fine for me, however. Battery usage of the internal strobe is greatly exaggerated in some circles. I run mine at half power which is more than enough to fire the externals and get over 400 frames off a charge. The Oly housing is made from plastic, while those others are metal..... IDK how important that is since camera housings are not generally subjected to abuse that would break even plastic.......
To address the OP's question, the Oly housing has three 1/4-20 bolt holes on the base to accomodate both center-mount and dual-bolt bases. Get a dual-bolt base... all sigle-screws will spin regardless how tight or what you put in between. I got Sea and Sea arms (NOT recommended, but functional and CHEAP...) which only come with a single screw.... had to drill 2 holes in the base to accomodate SS screws I got from Home Depot. No amount of tightness and rubber would otherwise cure the spin when wet.
For my money, I'm on the Olympus housings....