The right side of that looks suspicious. Get more light on that spot. It's probably just a shadow caused by that casting flash line that starts in the middled.
This is one of a million reasons to deburr/deflash a block when you have a motor apart. Cut down flash and then when you do...
Looks like casting artifact. A crack would be much more defined and start at a stress riser like sharp bend in the casting surface or near a main cap bolt hole.
You're digging into minutiae that's not easy to find accurate information on unless you have access to a lot of GM internal documentation.
All of the 4T64Es have the same gear ratios for the gears. The final drive might vary. The SSEI was supercharged and the car was heavier than the GTP, but...
It should be a T65E. It's the same gearbox as the 3800 powered Grand Prix, NA and supercharged. The T85E from the Northstar powered Cadillacs can also be made to fit, but it's a project.
Google or call your local parts store or start hitting up scrapyards.
Made it there and back again:
https://www.optimabatteries.com/experience/blog/2025-optima-ultimate-street-car-invitational-results
Finished 11th in GTV and 54th overall. Not shabby, best finish at the Vegas event I've had. Transmission gave me fits all week, suddenly started running really...
Module failure. They're all old and the capacitors are giving up.
You might be able to pull the module and take it a TV repair shop and see if they can re-cap it for you.
Yes, pan rail or slightly higher. You need to make sure the level is where the filter is submerged with the car running and the transmission at operating temperature.
Yup, I had to tweak the fronts. The QA1 shocks didn't have enough valve to control the 750lb springs I needed to keep the nose off the pavement under braking, so I swapped out for Viking Berzerkers. I had enough local autocross events this year that I was able to really dial in the shock...
The stock wastegate is a single-port that used a vacuum Y fitting with a restrictor in it. If you don't still have that part, it won't work. It doesn't work that well anyway.
You want is this valve:
https://diyautotune.com/products/ebc-solenoid-kit?_pos=1&_sid=2c40ed99e&_ss=r
You can wire it...
between '18 and now, it's got completely different shock/spring package, newer turbo, and much better tires. Plus a lot more seat time. It all added up.