[oldbluesplayer]

a couple more things - first - I'm gonna guess we are talking about the ubiquitous 350 chevy small block -

if that's the case, the basic 350 block comes in two versions, the difference having to do with the number of bolts holding the crankshaft bearing caps in place - they are what is referred to a 2-bolt, or 4-bolt, mains. The 2 bolt mains are the common car variety blocks. The 4-bolt mains are used on the heavier trucks, and the high output motors like the Corvette - these are also sought after by drag race guys, as they are much stronger.

To my knowledge, the blocks that are diverted to marine industry use up front, ie. that go to Mercruiser et al, are all 4-bolt mains blocks, to provide increased reliability - the typical boat useage does place a higher continuous stress level on a motor - cranking along at 3000 to 4000 rpm for long periods under load, where the average car use would be floating along at 2000 rpm, under a lighter, rolling resistance, loading.

Also, for the 350 small blocks, depending on the vintage, as these have been around for half of forever, there are a variety of heads available, depending on carburated, or FI, and these contain different configuration intake and exhaust ports, and often different sized valves, from each other - the high output Corvette motors, for example, use different heads than a sedan or station wagon motor.

Along with all that is the already mentioned camshaft differences, and the marinized electrics, starter, distributor, etc.

hope that helps some.

Bill