One quick observation. You are using Vortec heads. Since they are a fast burn chamber design you cannot run a lot of timing like you normally would on a BBC. 28 degrees total advance is about the maximum you can run. It's possible you detonated it right off the bat if you had a lot more timing initially. Maybe broke a ring land, torched a piston or tuliped some valves.

Bob Lloyd

I would say that the rings are broken. No way the smoke is from the valve stem seals.

Read an article way backed that talked about if an engine runs too cool the rings don't seal correctly and can cause blow by,, maybe not to that extreme though,

Were the cylinders plateau honed?

You said 2005 Vortec heads. Dumb question, but in 2005, wouldnt the vortec heads be off a 496 GM engine? Or are we talking about the oval port vortec 454 heads?

If its blowing oil all over, and compression test is showing 70psi,its time for it to come apart.

i may be wrong but i believe the vortec 454 came out in 96.the 95 is a gen5 engine,not a vortec.

Yes that's right mike. The vortec head was released in 96 along with the gen 6 block. The 1996 454 that came in trucks is completely different engine than the flat tappet , low 7.9 compression peanut port headed tbi injected pre 96 454. The vortec engines were 9:1 with hyd roller cams and mpi. In the truck world, the 1995 454 was something like 230hp and 385ft lbs. The 1996 454 was 290hp and 410ft lbs. The marine vortec version simply had a different intake setup and rated at 310hp. The marine version of the 1995 and earlier peanut port had a different cam and a carb. Rated at 330hp.

The 8.1 was referred to as a "vortec" also. I don't even think a 8.1 head would bolt on a 454 block. I assume he has gen 6 vortec heads. They do NOT like a lot of timing. I'm also pretty sure if you bolt those heads on a older block you must use the right head gasket. If the wrong gasket was used, water flow would be all jacked up. Prob overheating the block/heads from a water flow issue. I'm not certain on what mods are required to make that work ? That might explain why after 7 minutes it all went to $hit.

What was the piston to wall clearance ? I think the reason it starts running worse after it runs for a while is because your vent tubes from the valve covers are putting oil in your carb. Also that is very low compression.

If for some reason the head gasket didnt block the front water hole in the block, the water will bypass right thru there, coming out the thermostat housing. The rest of the heads and block will not cool, and overheat, but the temp gauge sender will still see water flow, and think all is well since its located at the Tstat housing area.

newer rings these days are looking for a very specific cylinder wall finish, no longer can you just scuff and install most of the rings now, you have a issue(no ****) in the pistons/rings, could be the hone job, the wrong ring(size/type) were they file fit rings ? or just plan screwed up on the install...