As this is the past subjunctive for "conhece" as opposed to the present subjunctive, would a better translation be "I would like for you to HAVE KNOWN him"?
yes, another correct option. Even though, if one saw "I'd like you to meet him" we'd transate that in subjunctive in the same (gostaria que você o conhecesse). That happens because it is a more literal translation, but both would be the same (the person still has the opportunity to know him). But if one say "I'd like you had known him", then it is "Gostaria que você o tivesse conhecido" (that is, the person has no longer the opportunity to know him).
"Gostar que" is more common than "gostar se". Also, "gostar que" show it is much more likely to happen.
Você gostaria que ela te conhecesse? VS Você gostaria se ela te conhecesse? (less likely)
Você gostaria se a Amy Lee entrasse por aquela porta agora? (it'll probably never happen to me haha)
My biggest frustration with learning Portuguese on DL has been "Eu gostaria" sometimes being translated as "I would like," and sometimes being, "I wish." Whichever one I put is often wrong. Can someone help me with this? Is it my Portuguese or is it DuoLingo? In this case I typed "I would like for you to know him," which seems right, but it was marked wrong. I do understand how it could be, "I wish you knew him;" I just think my answer is also right.
"I would like for you to know him" sound like a literal translation from Portuguese. Do you mean "I would like you to meet him"?
In order to distinquish translations of "I wish" and I would like" in Portuguese, you have to depend on context (hard to do with free-standing sentences in DL). If you check translations in linguee.com, you'll see various examples, sometimes using "queria" and sometimes "gostaria". The distinction between "would like" and "wish" is not so important the last two examples.
• I wish I knew the answer to your question.
• Gostaria de saber a resposta à sua pergunta.
• I wish I knew what the secret was.
• Eu bem queria saber o segredo.
• I wish I had had the training years ago.
• Eu gostaria de ter tido o treinamento alguns anos atrás.
• He said that he wished he had more time to finish the work.
• Ele dizia que queria ter mais tempo para completar a tarefa.