I don't quite understand how you could get more torque by making the inlets smaller.

Are you thinking their is an air velocity effect?

Doesn't make sense to me....

it probly wouldnt be worth it becuase you'd loose top end to make more bottem end but u'd loose a lot of top end for a small amout of gain in low rev range. but than this done with a turbo im unsure of what the result would be

Can't see any upside in replacing oval port with round.

I have a round port A15 head, I had thought it would have more low end torque, and a bit less topend, counting on going turbo, the smaller ports would be made up for in boost.

Thats kinda what I've been thinking, the oval port head is superior considering airflow?

Why do you want the the A12 round port head on the 1500? I thought the oval port A15 head was supposed to be better.

What dundee means is that your inlet manifold on the current A15 head (oval port) will have to be changed to suit the round port head- so round port manifold with round port head, and oval port manifold for oval port head.......hmm

As for the cylinder head, the bolt distance is the same.
The installation is possible to A10 - A15.
But I am different from an inlet port in stats.

elaborate as i am stupid

yes they are interchangeable, but the inlet manifold will need to be changed to suit..