Nothing new to offer... I use Black RTV (by permatex) "Max Oil Resistant". 3/8 bead across the china walls, and a heavier dab in all 4 corners. Never a leak.
I've put together a good few SBMs and never had this problem before which is why it's annoying. The 360 in my truck has a Performer intake and that hasn't leaked at all in the 3+ years it's been together but that has factory iron heads. The weird thing is both times I've sealed this 5.9/360 it leaks from the exact same spot, the passenger side of the front china wall.
To further address the blowby concerns the engine runs like an absolute champ, I had it chassis dyno'd back in Colorado and it made 286 HP to the rear wheels uncorrected which is pretty spot-on for this combo. After getting it re-tuned for lower altitude here in Georgia it now spins the tires all the way through 1st gear and will break them loose even from a roll until I either let off or shift to 2nd and that's with 3.55 gears, fresh Sure-Grip and 275-wide ultra-high-performance Continental tires. It frickin' rips and I need to have my wits about me before flooring the gas pedal.