Also I think we may be on to something about the rods being KIEKHAEFER's.
Just found this flywheel on ebay. Looks just like the one I have.

KIEKHAEFER HAYS FLYWHEEL 396 427 MARINE

that flywheel proves the engine was in a boat that uses a rear mount starter,my guess is trs application that is internally balanced.looking more and more like a old 482.did you measure the bore and stroke.

Well the cam has been changed at one point. Original specs are 288/296 and it now has a 290/300 and its all roller.
I guess after thinking about it (the sleeve) I guess it had to been taken apart at some point but man they put it back together right. RTV was only on the pan ends. When you take apart a 40 year old motor and all the gaskets just peel off leaving nothing behind it had to be done right.
Looked up the original head gasket. Hi-pro marine. Another thing that says it was a boat motor. So now I’m leaning toward it’s a boat 482 race motor that someone added a few tricks to.
Bore is 4”, stroke is still up in the air yet being the crank is at the crank shop. I have to call them today so I will ask for it to be measured.
anyone know what years the 482 were built? After looking up the Cyclone I ran across someone who said that the Merc Tornado was also a 482.

the bore can not be 4 in,std bore on a 427 or 454 is 4.250.

sorry, left off the .250 part

just a minor detail!

Never heard of the "Tornado" engine. But the 482CI 460HP engine was built from around 1982-1986. I don't think Mercury High Performance had anything off the shelf during that period, that made more power than that. In 1986, the 575 came out.

I agree with Mike Tkach. That flywheel is from a boat that used a transmission, like a TRS or Speedmaster. If someone was in there and installed a roller camshaft, I doubt that was done 40 years ago!. My guess is that engine is from 82-86 era, and has been recently gone thru.

During that era, they made the 370/400/440hp 454CI versions. One thing I see different in my service manual, besides the obvious stuff, is that the 482CI had larger valve seat widths, and larger bearing clearances on both the rod and mains, over the 370/400/440HP engines.

I hear you Mild but ..... hold on this is where we make another unexpected turn ....
The block #'s date it from 68-76
The heads #'s date it from 69-72
The Marine Intake #'s date it from 1969

In my searches the 340220 block shows 427T from 1968 to 1985?

http://www.strokerengine.com/BBCcasting.html

http://www.gmclassicmusclecars.com/bbc-block-s.html

I do agree the closed chamber heads would not have been OE on a mercruiser 482ci/460HP offshore engine.

My merc service manual states the 482/460HP cyclone static compression ratio to be 9.2:1, and use the same cylinder head casting as the 370/400/440HP engine, except those had a 4'' stroke, and were rated at 8.8:1 with the 118-119cc open chamber heads, which makes perfect sense when you calculate it.

It sounds to me someone swapped the original heads out for those closed chamber versions, to get the compression up around 10:1. With some cleaning up of the block decks, head decks, it may be closer to 10.5:1. Only way to know is CC the chambers and measure how far the pistons are in the hole. Im sure its gonna crackle pretty good at idle. I'd run it cool, watch the amount of timing, and use good fuel.