My curiosity got the best on this one and I'm impatient which led me to do some reasch on this oddball engine.
I found quite a few different versions.
They were used primarly as a bus/heavy duty truck motor but they did manage to find their way into quite few 1/2 ton pick-ups due to a V8 engine shortage in the mid sixties.
The engines were produced from 1960-1974
The largest of the V6's was a mind numbing 478ci :shock: with a bore of 5.125 inches and a minuscle stroke of 3.86 it was all torque.
Peak Hp was only 254 but torque was a very respectable 442 ft lbs @1400rpm.
Everything on these motors was overkill, shaft mounted rockers, thick decks surfaces, large journal forged crankshafts, smoothed combustion chambers to reduce carbon deposits, weight matched forged rods and 4 ringed pistons coupled with large capacity cooling systems and high volume oiling, these engines were built to last.
GMC marketed them as a low maintenace 200,000 motor.
GMC also made a V12 or a twin six, it looked like two 351 V6's mated together, but it was all one block with one crankshaft and one cam.
It did have four separate heads, four exhaust manifolds and 2 intakes.
Dsplacement 702 cubic inches! Hp was still down @ 275Hp but again torque was king @ 630 ft lbs.
Though it was used primarily in industry and in a few large trucks some crafty folks shoe horned them into some pretty neat stuff.
Click on the link to see the multitude of things these strange motors have powered.
http://www.6066gmcguy.org/V6powered.htm
Have a good weekend, Cp