We have a boat with two 534 Seamaster engines installed in 1972. They now have 2800 hours on them and still run great. They're rated at 277 hp and have a torque of 492 at 2000 rpm. Only problem: they sure guzzle gas.
Yes, one is counter rotating. They did have the Holleys but I had trouble getting kits to rebuild them so I bought 2 Edelbrock marine Carboraters. Therefore, can't use the governor linkage but still use the tachometer and that works fine. Did have trouble with the reverse rotation engine when a broken valve chewed up the head pretty bad but not the piston. I Got parts at a local junk yard for the repairs from an updated 534 engine. Updated parts included intake manifold, cylinder heads, distributor and water pump. I was told by a Ford dealer that the update was prompted by pollution standards in 1976 in CA. The new design supposedly makes it breathe better but I can't tell the difference. I would like to find parts to update the other engine but so far hard to find. Thanks for your comments.