I'm absolutely going to do a compression test as soon as I get home. Just wanted some input if I was goin in the right direction.

What is your oil level doing? Could you be diluting it with gas from a float set to high? How does the oil smell?

Do a leak down test. No sense in quessing. If it's pushing oil out, you have too much pressure.

Who's valve covers did you use,is their baffles in them? the carb will just ace like a vacuum cleaner with out them and suck oil from the valve covers..you cam tell from the look on the carb if its getting saturated with oil..

Last time I saw a fresh eng puking oil, turned out one of the ring lands was broken. Probably happened when pistons were installed and the ring compressor wasn't sitting perfectly flush with the block.

Did YOU build this motor or did an engine shop?
If an engine shop put it together bring it to them to figure out. DON'T take it apart yourself as they may use that as an excuse to not warranty there work.

I agree it sounds like a installation issue with the rings. Maybe installed upside down or in the wrong position. Compression test should tell the tale.

I built the engine myself... And yes I know when you hear that, most peoples reaction is "well you obviously ****ed it up, should have taken it to a professional shop", but I happen to run a shop myself, and have built more engines then I could ever dream to count, and have never had one turn out bad what-so-ever, so I'm fairly confident it isn't an assembly error, but then again nobody's perfect so I guess I'll be re-tracing every step here in a day or so. I compression tested it a few hours ago and it was 70, 80, 75, 85, 70, ect...... So basically that's Junk, junk, junk, junk, ect..... The cylinder walls were beautiful when I originally took it apart, so I did a quick hone on it, kept the factory bore, got new flat top pistons, and new Moly rings, and even used high zinc, non-synthetic oil to break it in. I know for a fact I installed the rings with "dot side up", (I'm kinda OCD about things, so I checked it about 12,483 times before I popped them in the bore, and I have a really good piston ring compressor, and they all went in smoothly), so I really kinda doubt that something went wrong there? They are Mahle rings, and I've used rings from them dozens of times in the past with no problems, so I wouldn't think there is a problem there? IDK, the only thing I didn't do "myself" on the whole build is the assembly of the cylinder heads, and the heavy-oil-smoking on initial startup has me thinking valve seals or guides, but even that's far fetched. The valve covers I'm using dont' have baffles in them, but are eddie-marine tall bbc valve covers. they didn't have any holes in them for breathers except for the oil fill cap, but I cut holes and installed baffeled breathers that vent to the carb, but the smell that comes from the valve covers after it's warmed up isn't normal oil-burn smell, it's like bunring aluminum smell or something... And the whole running awesome for 5 minutes and then slowly loosing RPM's until it dies is a whole other problem waiting for me after I fix the oil problem too... So I guess my main question is, I'm gonna go ahead and pull the motor here in the next week, and if the rings end up being junk, which I'll honestly replace anyway if I need to, what do you guys think I should do to prevent this again? Different oil? What kind of break in procedure? Again, I've done tons of new engines, but never had one do this, so if I'm doin something wrong I would love to know so I don't do it again! lol LOTO shootout/poker run is comin up!

Did you use hyper pistons? The top compression rings need a little extra gap with some of those, especially in a marine eng.
Hopefully that's not the issue, just throwing something out there.

What a pain in the a##. I had a customer bring in a 468 with a similar problem. When we pulled it apart, it looked like the rings never seated. He said he had a nice cross hatch pattern,but it looked like the cylinders polished back up before the rings had a good chance to seat.I checked the bore dia. and it was fine so we honed it again. Used Childs/Albert rings (with standard tension oil rings instead of the low friction he had used)and it's been trouble free for about 300+ hours now. ps some break in additives give of some crazy smells when they get hot!