Yes according to those casting numbers they are from 1968-69 396 & 427 390-400hp. They should have oval ports and closed chambers with the small 2.06 and 1.72 valves. Not bad heads, but in my opinion they may be worth something to a person restoring something and needing period correct heads. For your boat application, it all depends how much power you would like to make. Heads are a very important choice, for something in the range of 450-550hp around 6,000rpm open chamber massaged oval port heads. ie 049 or 781 castings with the upgraded valve sizes 2.19 & 1.88 will work fine. For anything above that power and rpm I would go with rectangular port open chamber with 2.19-2.30 intake valves & 350cc or larger intake port volume. Also never forget any head choice has to work along with your compression ratio, cam selection, rpm range, induction and exhaust system also your jet pump set up. Take your time and put together a good reliable combo...best of luck.

The L88 427 was actually a pretty radical engine for being production. It came with rectangle port aluminum heads, forged 12.5:1 compression pistons, solid lifter cam, forged steel crank, 7/16 push rods and the (big boy) dimple 7/16 rods with the boron steel bolts. The L88 and ZL1 were the same engine accept for the aluminum block.

Didn't they make about 560 hp  in stock form with headers and a good tune

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Good point  so with some newer aluminum heads and a nice hyd roller  and about 10.5:1  I should still be in the low 500 hp range    I want it to run  but still be friendly enough to cruise down river and come back   maybe a little Nos  to make her scream

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Sounds good, since this is the begining of the off season, why spend money going through the Olds engine when you seem to really want a nice 427 or any BBC? Why spend money on two engines? If it was me, I would yank the Olds and clean things up and get ready to build the engine you really want. Another thing on those heads, for me, I have never been a fan of the early closed chamber heads, they were looked upon as dirty burning heads due to the large quench area. Plus the small chamber shrouded the intake valve and hindered flow. The first open chamber heads were aluminum and introduced on the revised L88 in 1969 and also used on the 1969 ZL1. That design later found it's way into the iron castings in 1971. There is a reason that all aftermarket BBC heads are open chamber design, they work rather well. So like you said, perhaps buying an aftermarket set of heads may work out nice. I'm sure you will put something nice together weather it's a 427 or larger, do it once and do it right and maybe I will see you on the river... .. ..

The olds runs pretty good    I'm thinking it may need bearings    the last time out it ran the best it ever has  but I   ended up with water in the oil    if everything measures  correctly I'll  change the bearings  and maybe through a cam that I have  that came out of my 442

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