I think the only form actually in use is the racemate. Although the 2R isomer is x5 morphine (in animal models), the mixture comes as 75mg tablets which are purported to be around the same efficacy as 10mg morphine sulfate. Some further research revealed that the o-F & o-CF3 were twice as active and had a much higher TI (the original paper had stated o-Cl was optimal).
The pyrrole ring has also been substituted with a lactam. This is interesting because the =O is in the same spatial position as the 6 position in the phenanthracene scaffold. I seem to remember that some of them were rather potent.
If nothing else, the N-di(sec)butyl moiety is totally unique (activity drops off rather steeply when this pattern is modified). I have, in moments of true boredom, wondered if this pattern has ever been applied to the 3,3 diphenyl heptanones (for example) because the piperidine analogues of viminol were actually reasonably active. I don't think any antagonists in the methadone class have been discovered yet... it may just yield a little more insight into the pharmocore.
Unusual chemically & possibly useful in opioid detoxification but I don't think they have any subjective effects to make them worthy of detailed investigation.
BTW Viminol seems to have acute toxicity similar to that of other opioids although the analogues with different ortho substitutions had much, much higher LD50 values in the animal models at least.