http://www.revhard.com/parts.html
suppose to be a T3 on the Z31. From what I've heard, Rev Hard makes a quality manifold for the T3, T4 series turbos. Which most/all manifolds for the 240 is for the T3, T4 series turbos. Unsure if it is top or bottom mount.
I have driven an Talon ESI and boost felt more like it kicked in around 2800 to 3000. But I didn't drive the DSM but a time or two. I don't think you will find anyone making a manifold for the mitsu turbo charger. Someone correct me if I am not right....
What exactly are you wanting to do, power out put??? The T3 out of a Z31 is the economical way to go. And I don't you will be up set with the minor lag on the t3. IMO I would not go with anything smaller than the T3 and personally I would go with one of the T04 series turbos if I had the money.
Surely there is some other members here with more experience with turbos than I am, that can be more helpfull than I can, that will hopfully answer up.