I want to say that the spacer plate I sent Bruce with the flex plate was about 5/16" thick, just by memory. If anyone knows that the plate for this installation should have been considerably thinner, then we may have found the culprit.
My memory is exceedingly vague, but from my best recollection of taking a couple of 6-bolt BW35's off, the spacer was really thin. Almost like a sheetmetal cap. It wasn't sheet metal, but very thin.
Take that recollection for all it's worth (price paid, heh).