You were hoping for the 250 inline-6, right?
I'm quite sure the engine line up went like this;
I never saw a 3 on the tree or 4 speed on any of the V8s.
I think the 307 and 327s were gone after 68.
250 cid I-6 150 T250 & 3 on the tree.
350 cid V8 250 T350
350 cid V8 300 T350
396 cid V8 265 T400
427 cid v8 390 T400
The big dealership in the Peg back in the day was Holiday Chev Olds.
The Haddad's sold and opened Surrey Flag Chev.
I remember Holiday out on W Portage! But how about Terry Balkan Chev-Olds (with Brother Lou)? "You betcha!" Weren't they downtown on the W side of Main St? I bought a float for a Rochester 2-bbl there many years ago.
The 307 was the base engine for the '68 MY only - it succeeded the 283, and was replaced for '69 by the 327. It soldiered on until, I believe, 1973, where it could still be found in the Nova, but 1968 was the only year it was offered in the full-size Chevys.
I believe the 327 was gone from the full-size line up for 1970. (I know there was one in '69 - in '82 I transplanted a 327/TH from a '69 into my '68. The 327/TH replaced a very tired 307/Powerglide.)
I didn't even know there was such a thing as a TH250 - live and learn. Also, at one point I owned a '71 Biscayne - it had the 250 inline-6 and a 2-speed Powerglide, so I'm pretty sure the Powerglide was still offered in the full-size lineup in '69.