OK, then with a 350 balancer AND a balanced flex plate, we're running an internal balanced engine. I didn't think they existed in a 350 block
They don't. The Chevy small block used to be considered "internally balanced" but most of them weren't. Only the very earliest versions were--265, maybe 283. And I'm not totally sure about those.
They may use a neutral-balance damper, and a neutral-balance flywheel/flexplate, but most or all of them still got a counterweight formed into the crankshaft hanging out the back of the block. Therefore, they're "externally balanced" at the rear, but using a neutral-balanced flywheel/flexplate. Same with the 366/396/402/427
Of course, the 400 had external balance at the front and the rear, because both the damper and the flywheel/flexplate were not neutral-balanced. Same with the 454.
And then the one-piece rear main engines got neutral-balanced dampers but offset weights at the rear because that counterweight that used to hang off the rear of the crank can't be there any more or the seal won't slide over it.
I went nuts trying to get the one-piece rear main seal 350 in my K1500 balanced--the two aftermarket flexplates I bought were weighted differently, and neither one matched the OEM one-piece seal weighting. BE CAREFUL about which flexplate/flywheel you use on a one-piece seal block.
Decades ago, I put a 400 small block in my 'Camino. Aftermarket crank, rods, pistons. I gave the balance shop a standard "400" damper and flexplate. Turns out that engine was easiest to balance with a 400 damper and a neutral-balance flexplate.
In short...put on the parts that 1. fit properly, and 2. actually balance the engine.
All 1-piece rear seal SBCs and even 4.3Ls have a counterweighted flexplate or equivalently balanced flywheel to my knowledge. My 383 is just like any 86+ SBC, neutral balance front, counterweighted rear. That would be internal balanced front and external balanced rear.
Yup.
- may need reverse flow water pump
No such thing, that I'm aware of.
There's water pumps intended to have the impeller spin the same direction as the crank (early engines.)
There's water pumps intended to have the impeller spin the opposite direction as the crank ("reverse
rotation" pumps, driven from the smooth side of a serpentine belt.)
But the FLOW is always the same--from the inlet of the pump, to the outlet where it meets the block.
Note that some SBC ENGINES--blocks, heads, head gaskets--are intended for so-called "reverse flow", but the water inlet on the block is in the standard location. The internal passages are revised so the coolant gets pushed "up" into the heads right away.
Pontiac also had "reverse flow" from '55 to '59 or '60. But they had the coolant coming out of the water pump enter the heads directly, not the block. International went to "reverse flow" (which they called "Improved Cooling") on their later 392 truck engines, but never on their 345, 304, or 26x versions. It was more like the Pontiac system than the Chevy system.
Both Pontiac and Chevy got rid of "reverse flow", International used it for a few years and then pretty-much went bankrupt.