I have an '84 Sea Ray Sedan Bridge 300 with "fraternal" twin 260 Mercruiser inboards (5.7L/350 Chevys) and V-drives. She stays, and plays, in saltwater (closed cooling). The starboard engine's port riser failed (corroded internally where it meets the exhaust manifold) and overheated the engine awhile ago. I didn't realize what had happened at the time and I let the boat sit. The port/even bank of the engine got saltwatered and, of course, seized. I got the heads off the other day and the pistons are beyond ugly, but from what I can see so far, the cylinder walls look o.k. I'm going to try and get the pistons loose, and out, and see if the engine block can be saved (bored).

Assuming I can get the pistons out, I'm contemplating rebuilding it as a 383 (6.2L). I figure since I'm already pulling the engine, boring the block, buying new pistons and rebuilding anyway, all I need add is a 3.75 stroke crank and a 400 harmonic balancer and then have it balanced with my flywheel to get a 383. Or, maybe a rotating assembly kit. I figure parts and machine work to rebuild the 350 is $700, and $500 more than that to make it a 383. Rebuilding either a 350 or a 383, any advice on compression ratio? Book says my 350 is 8.5 to 1; any problems bumping that to 9 or even 9.5?

The questions I have are:

1. I would prefer, for now, to leave the port engine as is. It’s a remanufactured with low hours installed four years ago. Money is real tight, and I am going to replace all four risers, too. Are there problems using a port (reverse rotation) 350 and a starboard (standard rotation) 383? Perpetually turning to port? Transmission problems? Vibration? Props fly off? Boat flips over? I’d rather rebuild this engine once and not have to pull it again down the road just to replace pistons again and change the crankshaft. Can I run mismatched until I get around to converting the port engine to a 383 also, or do I have to convert both simultaneously? (BTW, Can I pull the crankshaft with the engine in the boat? Doesn't look easy.)

2. Are there problems converting the port reverse rotation engine to a 383? Is the reverse rotation crankshaft any different than a standard rotation one? The throws are still 90o apart and the firing order is exactly reversed, right? I would assume a balanced crankshaft is balanced regardless of which direction it is spinning. Can I install an aftermarket 383 crank from Summit or Jegs? Did Mercruiser build a first gen smallblock 383 (two piece rear main seal/internally balanced)? How would the 350 camshaft behave in the longer stroke/10% bigger 383? If I have to upgrade the camshafts, can I even get an upgraded reverse rotation 383 cam for the port engine? (Can I get an upgraded reverse rotation 350 cam?)

3. Why is the flywheel on the existing engines indexed to be installed in one specific position? To me that implies that the engine is externally balanced. But, first gen smallblocks are internally balanced and use interchangeable flywheels and balancers. So, I'm confused. And so what does that mean is needed to balance a new 383 assembly with the original 350 flywheel?

Happy New Year!