L67's were the training aids in my upper and lower engine class, along with me having a modded one in my Regal GS, and I can vouch for how absolutely stout they are. Like the others have said, the pistons are the only factor-you'll NEVER break the rods or crank in one of these. Ever. The only thing you'll ruin is the valves, head gaskets or pistons if you're under WOT with super lean conditions and/or insufficient octane. Had a classmate build an L67 from the ground up, then put a 2.8 or so pulley on it (which is super small in our applications) with no meth or high octane and blew through a piston on the freeway within a week's time. Other than that, if your tune's on, you'll blow thru 25 transmissions, 43 cv axles, and 40 passenger side front tires before you ever put any appreciable wear on a nice L67.
I'd be willing to wager, of course if everythings set up right, that not only will you best every record that a factory 109 block has, but your car will rust out around that engine before you need to replace something in it.