I'm pretty sure that you can put in Ej25D cams but given that they are NA they probably wouldn't be all that great for what you are doing.
If I had those heads what I would do is go on Ebay and look for some HKS or Kelford cams for the Ej20k. Or find a vendor with an account with one of those companies and order the cams in from overseas. You could also try going directly to MRT. They will ship to the states and carry a lot of that kind of stuff.