Hi! I'm a long-time lurker, first-time poster. I have a number of old Macs, and got a working SE/30 a couple of months ago. I, too, have been looking around for a network card, and have ended up with three of them! I have two Shiva Etherport II cards (one branded Novell), both with the 'Kinetics SE' back panel board, with only AUI and 10base/2 outputs. I may start another thread about building an RJ45 panel for these, as I don't have any means of connecting these to a standard router at present, and would rather not use a AUI to RJ45 transceiver.
However, I have recently found a Daynaport E/Si30 board, but without the back panel board (with the AUI/BNC/RJ45 connections). I don't fancy my chances of finding the back panel board on it's own online, so I'd like to try and build one. Also, I've seen these boards come up on their own before (ie without the back panel), or with an AUI/BNC version, so I think it's worth trying to reverse engineer a board with an RJ45 connection. I've seen a few other pictures of these boards, but yours (kingchops) is the first I've seen with an RJ45 10base/T port. The BNC/AUI version has a few passives on the back, but I think these are for the BNC connection; see
http://www.recycledgoods.com/dayna-e-si30-ethernet-card-w-daughter-board-ribbon-cable.html. There's also an area on that board for the RJ45, with space for a bunch of passives. I've got another ethernet adaptor which has the same SONIC-T chip as the E/Si30 (it's an Apple Comm slot 1 ethernet board), and there appears to be very few additional passives and connections to the RJ45 port, and roughly equivalent board components. This makes me think it should be a relatively simple connection... I hope.
What I really need is a good picture of both sides of your back panel board, as clear and zoomed in as possible, ideally so I can read the values of any surface mount resistors. This will hopefully make it clear what connections need to be made. Ideally, tracing the pins of the RJ45 back to the ribbon cable connector would be perfect, but I don't expect someone to do that for me! Any help would be greatly appreciated.