I had the car weighted yesterday for the first time so I don't have a before/after. This was with 3/4 tank of fuel since that is where I run it during autocross. I just wanted to get an idea where I was at.

Here are the numbers:
Total: 3386
LF: 877
RF: 905
LR: 792
RR: 812

I really thought I'd be over 3400 with all the stuff I added over the last 2 years. Had the fuel tank been full, I definitely would have been over 3400.

https://i.postimg.cc/FHQKFspp/IMG-2492-R1.jpg

Yesterday was a good and bad day - Good - 35 years ago on the 2nd Monday of August of 1989 I bought my 69. Bad - had a motor issue at the autocross on Sunday and last night trying to figure out what happened, my compression test showed the #5 cylinder has none.

Bought a borescope over lunch today and confirmed scratches in the #5 cylinder - looks like broken rings.

So frustrated because I had finally got my suspension / tire combo figured out - Sunday was the most balanced my car had been in 2 years. It had been tight until last month when I added more camber and softer front tires - that made it really loose. Changed the rear tires to match the fronts - unreal the difference. I'm now running Falken RT660's - 245/40/18 front 275/35/18 rears.
Trying to decide fix what I have or buy a new short block?

Well, that's no good. Sorry to hear of the troubles. If you liked everything about the current engine, just repair or replace with like components. No sense in reinventing the wheel which will take longer and cause you more effort to dial it all in.

Took the motor out tonight and tore it down to get the #5 piston out. The 2 upper ring lands were broken. One piece fell off the piston. Thankfully the rings did not break so just some scratches in the cylinder wall. I believe I found the limit of Hypereutectic pistons. I'm thinking there are 7 more that might not have an issue now but soon will.
https://i.postimg.cc/QxvWS5TD/IMG-2575.jpg

https://i.postimg.cc/y893GdmZ/IMG-2577.jpg

Hopefully the scratches aren’t so deep that a quick hone and a set of forged pistons won’t get you back up and running.

Detonation?
 

Broken ring lands on a hyper piston are often due to detonation. Hyper pistons are notoriously sensitive to even mild detonation that you might not hear over a loud exhaust :-)

I had sealed-power Hypereutetic pistons in a motor I built in 2005, that had EXACTLY that failure mode... they looked identical to yours.

Tune conservatively with those hypereutectic pistons!

Yes - found out the Hyper pistons have their limits. With the upgraded Trick Flow heads I added this spring - I think I pushed a little past the limit of what they can take. There were no marks on the any of the pistons or exhaust valves the would indicate detonation - but it is possible i had some? Timing wise, the motor always liked 36 total (no vacuum advance). My compression is 10.4 and I always run Shell 93 octane. The motor was built in 2003 but only autocrossed for last 2 years.

I bought a crate motor from Summit on Friday with all forged internals. The manufacture of this engine states to set the timing at 34 degrees. I'll fix my existing short block as some point with forged parts as a back-up.

Still working on getting the car back together again.

New motor is installed and running. It's a Blueprint 400 rated at 500HP. It's an all new engine with Blueprint's own aftermarket block. I have to say it's nice block with a lot of improvements over a GM casting - I really like that all of the head bolts are blind so no risk bolts/studs of leaking coolant. I had to buy a long block and switch the heads to my Trick Flow. The Blueprint heads have raised exhaust ports - 1/2" higher that stock. I didn't want any issues with my headers/exhaust fitting, that was the reason I made the switch.

I put about 60 miles on it now and it runs really good.

Purchased from summit 8-16:
https://i.postimg.cc/x1RJ6LG9/IMG-2579.jpg

https://i.postimg.cc/RVwnnkN6/IMG-2581.jpg

Prep'd and ready to install Tuesday afternoon. Motor and transmission went back in Tuesday night.
https://i.postimg.cc/DwF4QxXC/IMG-2587.jpg

Friday Afternoon 8-23 install complete and running:
https://i.postimg.cc/HLkJRj3X/IMG-1340.jpg

Looks very nice, congrats!!