Yea, I could have put in a small block but thats what most everyone does. I really wanted this build to be old school!I am not working on anything this winter. I am at the place in my life that is it needs more than routine maintainance, it gets replaced.
I do want to encourage you on having fun with a straight 6. They they can be fun. I took a ride in a truck that was a 300 straight 6, basically like yours. It had a trick valve job, a fat cam, a manifold that accepted a 4 barrel and true dual exhaust balanced split headers. It was amazing how hard that truck would accelerate. I always thought a straight six with a centrifical supercharger would be a blast, as you can make a mountain of torque without the kind of rpms that will bust up the long crankshafts.
In the sixties Pontiac sold a Tempest with an Over head Cam straight six engine with the 3 on the floor transmission option that would walk right past an entry level 326 Pontiac v8 (that admittedly was kind of a pooch)
There is a certain perverse satisfaction when you leave someone behind at a light and then have the opportunity to tell them, "hey, I only got a straight six"
Jaguar always did pretty good with a straight 6 that started life as a fire truck engine. "six in a row CAN go"