A problem on SB's is the oil rushes by the #4 main so fast that the oil has a problem making the turn & the rods on either side can & have failed. I ain't up on BB's but reportedly they can have a similar but lesser same issue (& their routing as you know is different). I would definitely open up the galley to main passages (Mcandless & others have writeups on this) & consider bypass direct feed the other end of the gallery. Just thinking out loud & I hope it works out (I am considering a 543 'source kit) but at the moment 2K for 100 extra cubes ain't practical right now.