Practically any stock LSx type motor will have the balls (torque) of a carb'd 350, maybe a bit less than a basic 383/400, but will be much more fun to drive. Slap on some bolt-ons plus a cam and they're much better than 40yr old carb tech.
They bolt to a th350/th400 with a few $ in easy to buy parts, and the modern trannys will adapt to the car nearly the same way. For a few bones you can get a full engine harness where you only need to feed the engine +12V and the ignition wires. From there you can stay stock-ish, or use the EMS options for bolt-ons, turbos, blowers, etc.
That's my future plan for by 67 bird, stuff in a 5.3L (since it's a 326 HO trim car) so its a quick DD, then build from there. The actual motor will only be 1/3 of the overall cost, so it's usually best to pick what you want.