I put a Service Replacement L05 Caprice engine in my K1500 back around 1998-1999, something like that. The L05 passenger-car engine has a roller cam, flat-top pistons but is otherwise similar to the L05 truck engine.
About 18 years, and ~80,000 miles later, the thing sounds like it has a rod-knock when I'm going to get Subway for supper. Very throttle-dependent. At light throttle, the knock went away (at first.) Loud as hell when accelerating.
By the time I got back from Subway, the knock was constant and constantly loud. No power. Wasn't sure I'd get home until I pulled into the driveway.
Head gasket blown between 3 and 5; the blowtorch effect of the combustion gasses gouged the block and the head. I might be able to salvage the block; but it'll take quite a cut on the milling machine to do so. There's no hope for that head. It's bolted to the back of my riding lawnmower to counterbalance the snow-blower attachment during the winter.
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I rebuilt a Vortec 5.7L short-block and put aftermarket cylinder heads on it.
1--8--4--3--6--5--7--2
Each cylinder is 90 degrees away from it's neighbor in the firing order.
#3 and #5 are 180 degrees apart.
Keep in mind that when #3 fires, #5 is getting toward the end of the intake stroke. #5 has nearly a full charge of fuel/air. The #5 cylinder is ignited by the #3 flame crossing the opening where the head gasket has failed. The #5 piston is near the bottom of it's stroke. Not only does the pressure spike on #5 try to turn the crank backwards while #3 is turning it the correct direction, it's very likely to ignite the fuel/air in the intake manifold too, because the #5 intake valve hasn't closed yet. If the intake manifold fuel/air ignites, #7 and #2 could get a contaminated air/fuel charge.
Yeah, the engine will have no power.