Well , lots of things will cause things to go through the side of a block, snapped timing chain is one of them, a rod that can't take the stress of the transition from push to pull. It's usually a rod or something in the valve train. But yea, a down shift too high in the RPMs can cause things to break.
Apparently one of these engines running an ATI super damper at Bonneville and it appears it simply melted apart (The ATI dampers are an inner and outer piece held together with large O-rings).
http://vortec4200.com/forum1/viewtopic.php?f=13&t=1020
One of the guys on the Vortec 4200 board (the above thread) had some dampers made up to cancel out all the harmonics to 7600 rpm. Looks like a nice piece, but $600 + dropping and machining crank + new bearings + new cap bolts since the 4200 is all torque to yeild and I'll be running a close ratio 6 speed so I don't know that I'll need the RPM range really.
A damper on a straight 6 isn't the same as an external balancer on a V6 or V8, it's intended to stop the rock. Inline 4s and flat crank V8s have the rock pretty bad, it has to do with the 2 center pistons up when the 2 outer are down, this creates an expotential moment and at the right RPM will travel throught the crank and and bounce back at the end it will increase the frequency each time it gets transmited through the piece. Ever drive I10 through Louisianna across that bridge in the swamp that goes on for miles and miles? I did, many times in a lifted Suburban, and at about 78 MPH you hit an expotential moment frequency and if you don't change your speed the truck starts to litterally jump off the pavement because the sag between pylons creates one of those frequency events. It takes maybe 5 miles or more, you give up on cruise control pretty fast. Anyway point is that this also happens in a straight 6 but to a lesser degree, firing order makes it the same sort of thing 1&6 are up followed by 2&5 then 3&4. Most V8s do not do this because they run an out of balance cross crank which kind of randomizes things, but limits the the overall RPM potential of the engine and adds a lot of weight in counter balances to the crank.
Even firing engines with odd numbers of cylinders per bank have issues that can only really be cured with counter rotating balance shafts. So singles, triples, inline 5s and any V with an odd number of cylinders per side and V angles that make them fire the same number of degees from each other. Just so you know only 60 degree, 120 and flat sixes for example naturally fire evenly if they are sharing a common crank pin. All 90 degree V6s either fire in a 150-90-150-90-150-90 degree pattern OR use crank pins offset 15 degrees forward or back from center on the same throw.
Belt drive would be tricky, it's not so easy to make the crank to cam chain area dry on this engine, you'd be back to all new billet engine front.
Hmm, maybe this is all too geeky, but I guess it points out why I find push rod engines kinda boring.
But just remember, if you've ever heard a story about an engine that ran so smooth you could balance a nickel on the valve cover with the engine running, the story probably referred to either an inline 6 or a V12.