Just another lucky day?
Well maybe, cruising the local online classifieds I ran across another 4-bolt core (w/std. flat top pistons & rods), and for just $100 bucks it was worth a look for sure. This one has a 10069286-casting number which is 90-91 454 4-bolt, Mark IV, short deck, the build date stamping is T06020XG T=Tonawanda, June 2nd, 0XG= 1990 Marine 454 310HP Inboard/Outboard 4BBL. As mentioned before these blocks were only cast as a 4-bolt main and are some of the very last factory Mark IVs produced.
Déjà vu we’ve several with this same 286 casting number, our K30 has one and the C10 motor currently at Fastlane Machine is another. Those are both truck blocks where this one is a marine block, the same thing just built for a boat. The plan is to keep this one for a backup and sell the 2-bolt main block we had from the motorhome (with all the flat top pistons, rods, and its original cast crank). If you don’t recall the motorhome block (link), that one looked like it needed a sleeve in cylinder #7. It was acquired at the same time as our 445 “Good to go!” block that’s being built for this project.
http://67-72chevytrucks.com/vboard/s...&postcount=128
I’m not a boat guy but I believe marine blocks usually use lake water instead of antifreeze as their coolant. This can be hard on the coolant passages (rust, sediment, etc.) but with a thorough blowout during the initial inspection, I think this block looks ok and should be a good builder if it's needed.