I went to show yesterday and saw a South African Chevy, based on an Australian RHD car, which had a 250 Chevy six. The bolt pattern looked like a T350, T700, etc, would bolt up. What era /models U.S. made GM Chevy's would have used this type motor.?
A six was an option on most Chevrolets, and it shared the same bellhousing pattern as 1955-up, all Chevy V8, including diesel, and 90º V6. L6 equipped vehicles from 1963 up, RWD Iron Duke 151 4-cylinder, 153 4-cylinder, and many Mercruiser marine variants, too.
I'm going to be lazy on his one and send you to this link. Scroll down to Third Generation. That gives the sizes of this engine series and a decent listing of what you might find that engine in. https://en.wikipedia.org/wiki/Chevrolet_straight-6_engine I had a 194 out of a Chevy II in my 48 pickup when I bought it in 1973 Reliable and fine for cruising but no power house, The 230 was in more full size cars, the 250 was in most models made from 74 until the late 80's I have one that is beyond worn out in the truck now. The 292 came in pickups and larger trucks. Taller block on it and pretty good torque. There is quite a bit of speed equipment for them but it is on the expensive side due to the low numbers they sell.