I can find the boat with twins, but I can tellyou with a single engine it is 4690 lbs. Sea Ray made a 250 Amberjack in '85 that had twins and was just over 6,000 lbs. Is it possible the boat you are looking at is an amberjack?
Don't know the weight but I do know those engines. I had the 488 version in my 83 21 w/a SR which put out 188hp. Whatever you do, don't overheat them or run them wide open. They are the Merc/Chevy configuration. Steel block with aluminum head. I've heard parts are scarce for these motors. It was pretty good on fuel though. Matt.
You can go to the Sea Ray website and they will have it on there. That is where I found out my weight when calculating towing. I found my under the owners manual which they have online.