Why not go on-center?
The only difference parts wise is the intake manifold
I have a complete motor being freshened now in the for sale section and it has an intake
When you space out the lower damper all the accessories will line up fine. You must pay attention to the details when assembling a On-center or you will be in trouble.
Mac In SD helped me with my on-center. Machine .125 off front cover and accessory bracket and everything will work. He knows his stuff when it comes to this.