A constant pressure valve body is really a race thing but I guess you could use it on the street if you can put up with the harshness. You don't state what you are put in front of the trans so it is hard to make recommendations on what you might need.
The 2004r can be made to handle plenty of power. A hardened stator support and sun shell would be on my short list for any overhaul. A larger servo, either aftermarket or one from a 200c could be substituted for more holding power for the band. Some good clutches and maybe an upgrade to three for overdrive. And a good valve body kit from one of the 2004r specialists.