Smoke tests were completed a while ago, which revealed a number of issues in the fuel injection and vacuum lines. All resolved. The issue at the tank is now resolved as well, pure ignorance on my part in fact - the pump had no rubber seal.
When I removed the old pump it had been more or less glued in with some kind of nasty non-hardening sealant. The kind of thing someone buys at Pep Boys and it never works. I cleaned all that up and never realized there was no rubber seal on the old pump. The black "seal" I saw in the pump collar wasn't the seal at all. I ordered a new seal thinking it was that black collar, but instead was a part my truck didn't have. Now it does. No leaks, evap works.
I now have a zero code throwing Disco 2. Quite happy about that and thanks to those who offered advice.