Nothing wrong with a 305. Got one in my 78 firebird and it'll scoot. Not as strong as what you've got...

mine is .060 over, stock heads, dual-angle grind, Comp cam with .454 int/ex, 290 duration, HEI, and (get this) two barrel intake and carb. It gets 18 MPG @ 80 MPH, and is exremely reliable. I had a 2.56 rear end with clutch limited slip, but it wore the tires too badly ( daily driver ) so I swapped it for a 2.41 open rear diff. @ 65 MPH I can drop it into second with no fear, and grab a car length before the other guy knows what hit him. Got a 350 turbo trans with a stiff shift kit, it'll gain a car length when it shifts from first to second.

The wife had a 318 in her 86 dodge diplomat, with similar build, but the 305 in the 'bird would smoke it everytime.