Quest to getting my Slant six to turn over

Alright to i have a recently purchased 225 1975 duster with a 727.

I put a new lead on the battery and tried to jump it. Amazingly the interior lights worked, the exterior lights worked but when trying to turn over all i got was a clank from the solenoid area.
I'm a complete nobody when it comes to electrical.
is there just not enough power going around to turn over the engine?