Have to agree I had a 74 a body that my mom bought new and the gears were way too high. In my 89 m body I just switched from 2.3 to 2.9 and the 318 is a LOT faster ( not saying much but I only take it yarding and .. ) so thats my 2c.
Now if I were building the motor I would have put more compression in it. RV cam and ported heads and low compression also not a good combo. When the motor was built did they tell you what the static compression ratio is? B4 you buy any new parts check the compression for me.