Let's see if this link works.

https://www.performancetrucks.net/forums/attachments/gm-parts-classifieds-23/52293d1274528758-rebuilt-317-heads-ls6-springs-0-miles-%24400-shipped-100_1339.jpg

the area where the head bolt holes are in the middle is wide open to the lifter valley. This is lower than the outer floor where you would drill for a drain. Again, I'll have another look this evening. making a clear valve cover for this would be easy and informative too.

Jeff

I may be able to offer some answers to "go-fast" SBC application.

I have a 1996 Fountain Lightning 35 with 2 Marine Power 6.2 LSA small blocks. The original performance report had the boat at 77 mph at WOT with the 502s. I have been able to achieve 80 mph at WOT with the sbcs. There is room to improve, I haven't tested the boat with minimal fuel yet. Engines have around 80 hours and are mated to Bravo 1s. So far, I have had reliable power, always fill with 93 octane fuel.

This help?

Maybe near valve spring rewards exhaust side

Most of the oil should run along bottom side of head toward exhaust side before it fills high enough to spill into head bolt holes. Your just looking to divert some of the oil from going to the valley. You could also plug a couple of the those holes towards the rear, maybe threaded aluminum plug or something that snaps in. Doesn't have to be perfect seal. Just some ideas. Good luck. Nice job by the way looks really clean.

Yep, just had a look at my heads. Looks like I can make plugs over the head bolt holes and add the external drains. Done deal!!

what shall I obsess over now?

Jeff

You get what you pay for! Merc gets a more reliable and less expensive to build with the BBC in the 400 plus torque.
yes you can charge a SBC to produce the same of a BBC. But you just hadded the cost of a charger and that charger can be added to a BB for the same cost has the SB.
Stroking is good but it also has it limits. Again cost vs gain....
The LS technology is great. But more $$$ and great gain.
It's all about torque for boat. Wile your torque curve climb, you are accelerating. Has soon has it peeks (regardless off your RPM) you are pretty close to top speed.

I'm all BBC no doubt but I don't think I would have had room for twins BBC in my last boat which had twin 350. Had plans for twin little M darts 434cu in, boat sold the boat

Whoa. Nice, 652hp that's gotta be up around 6500rpm? Correct