Recommend 284 twist and contour

I have a customer wanting to build 7mm-08AI on a 700 action. Plans are for a barrel no longer than 20" and he will be running it suppressed most of the time. Now, I've already discussed with him the negligible gains of the AI in a 20" barrel, so please keep that out of the discussion. He just plain likes the idea of the cartridge. He plans on experimenting with the Federal 155 Edge TLR bullet, so looking for suggestions on twist rate. Most readily available 284 barrels appear to be 1-9. The 155gr will probably be the heaviest he will play with. Will the 9 twist suffice for this.
Also, we are looking for the muzzle diameter of around .750" when finished at 20". What contour barrel will get me there without further contouring?

 

Number 4 or 5 contour depending on manufacturer. 9 twist would be good for up to at least 162 grain.