The path of least resistance would probably be to run the Honda 6 speed with the k20/24. The K series is a fantastic motor, but the trans is less than fantastic. They're known to fail even at stock power, also making them somewhat expensive... Not sure how it compares to an F35/F23. However, because you're going to use it to power something that's half the weight of an 8th/9th gen civic the trans will probably hold up fine in a goblin, but you should probably open it up and replace the syncros at a minimum. Particularly the early 8th gen Si's had a lot of syncro issues. They're fluid-picky, so I've seen a couple "bad" transmissions get "fixed" with some amsoil MTF. With that said, the factory LSD in the Honda trans is surprisingly good for a factory LSD IMO. If you would like to mate a K your GM transmission... Miata's have an ecotec and K swap kit available... but I don't believe patterns are published. It might be a good start to get a rough idea on the differences, though.