Those are my 3D printed block offs.
And as stated above. Anyone can post pics.

The cracks in my block

https://cimg7.ibsrv.net/gimg/www.off...193c772ae.jpeg

https://cimg8.ibsrv.net/gimg/www.off...57f2e2516.jpeg

Locknstitch. I have a 502 froze , bought it cheap. Scared up the stuff to fix the cracks. What is that block? Valuable or typical 454? 3D printed, so not metal? It'll hold 50-60 psi though.

It's just a Gen V that was bored 0.070" and has lasted 20+ yrs. 12 yrs at 600-550HP. It owes me nothing. 50-60 psi on plastic is no problem. I did seal them with Ultra Black.

A 502 or aftermarket and it has to be considered. That's why i think Tahoe needs to fab a pressure tester and see if the problemo can be isolated.

My head guy uses quite a few ProMaxx and really likes them out of the box for the price. (AFR 315 clone'ish) Might have a pair on the shelf, I know they have been getting popular and lead times are a little out.

I got 621 HP and 675 lbs of torque out of my 548 with 088 iron heads. I would have to assume a 540 with better heads and cam should bump me up enough to put a smile on my face. I will still go with a small dome piston to be around 10:1 mark depending on the heads.
Here are some of the pics of my setup and it really looks like the intake to head connection was sealed and the head gaskets looked perfect. I have looked over the block and heads with a very bright light looking for a crack or anything weird. I have not found anything. I really think it has to be from the 2 sleeves that were installed in holes 3 and 5. No other invasive machine work was done.

https://cimg1.ibsrv.net/gimg/www.off...490340522d.jpg
https://cimg2.ibsrv.net/gimg/www.off...07d4ce3c02.jpg
https://cimg5.ibsrv.net/gimg/www.off...96c40a14c6.jpg
https://cimg6.ibsrv.net/gimg/www.off...dd925818d1.jpg
https://cimg9.ibsrv.net/gimg/www.off...2acb534734.jpg
https://cimg8.ibsrv.net/gimg/www.off...534b37bb6d.jpg
https://cimg3.ibsrv.net/gimg/www.off...8472a350eb.jpg
https://cimg4.ibsrv.net/gimg/www.off...2db19c51ad.jpg
https://cimg7.ibsrv.net/gimg/www.off...04a1bc2dd8.jpg

Dude, why don't you spring for a set of head gaskets, bolt the heads back on and pressure test before you spend big bucks building another motor. If it turns out to be the sleeves they can be redone. It's summertime bud............

I have all the stuff to do it. I can put it back together sometime this week and test it. I do have another boat I bought this spring for the smaller lakes around my area and we have been having fun in that. This boat of heartache is strictly for Lake Tahoe.https://cimg4.ibsrv.net/gimg/www.off...a7f4736445.jpg

It is a Hallett with a BBC and jet. Unfortunately I have big motor plans for this one too. Wish I could leave things alone LOL. I did do an intake and carb upgrade to it already. Payupsucker that is one nice looking boat!https://cimg1.ibsrv.net/gimg/www.off...a03dd9e8c7.jpg
https://cimg7.ibsrv.net/gimg/www.off...7e655fc913.jpg

Thanks, it's a 69 Tahiti, bone stock original in excellent condition. I bought it 12 years ago from the guy who bought it new.

Any updates?

I do, I have bought a water pressure blow off valve to make sure I don't have too much water pressure and I have decided to install a set of Brodix BB2 Xtra CNC heads with Jesel shafts that I was saving for another project. The machinist thinks it was leaking at the head gasket, but is weird as I never had this issue before. I am going to test again with the new heads and using the same heads gasket I used on my drag race motors and those never leaked. I know the rockers are not on straight this was just to check pushrod length.https://cimg3.ibsrv.net/gimg/www.off...4e1bcdf46c.jpg
https://cimg2.ibsrv.net/gimg/www.off...65e8e779bc.jpg

thread seal the head bolts.......:D

Here is the update. The new Brodix heads with shaft rockers do not leak and the motor is really quiet. First time out we had to get towed back in as the motor overheated and died. I found that one of the new connection for the blow off valve had come off. Just hooked everything up and it runs fine so I think all the steam in the engine compartment killed the ignition. I also installed a water pressure gauge as well.https://cimg8.ibsrv.net/gimg/www.off...af1aab65dd.jpg
https://cimg7.ibsrv.net/gimg/www.off...d585b1fc06.jpg
https://cimg9.ibsrv.net/gimg/www.off...d803ce0c93.jpg

Glad you got it straightened out bud :-)

I am not sure, I did replace the 088 Gen V heads with Gen IV heads and known good FelPro 1057 head gaskets. I never had this issue before so I am having the 088 heads pressure tested. I never ran a thermostat and the only new piece from that wasn't from the old build was a new brass water pump. I have no idea if this would be any different from a plastic housing. I will get some pressure readings when we go out next. Oil is totally clean and no milkshake.