I designed a cart housing that is free to download on thingiverse: https://www.thingiverse.com/thing:5407426
it includes both a normal cart back as well as a version specific to the N64 adapter.
Also just like my other cart housing designs each half is also able to mate with the opposite half of an original cart housing.
I'd like to see comparison shots using the same game when you get a chance (N64 RGB VS Aleck64). It looks good to me.I also wanted to add this opinion:
Now that I've tested and seen what games look like on a cab through this board, I can confidently say: Don't go out of your way to get this for a JAMMA N64 solution. The video quality is not that great. It looks like Seta used a crappy MAX232 for amplifying the RGB video to TTL levels. It's still quite dark and you may have to turn the contrast knob way up on your arcade monitor.
You would be a lot better off simply using a consumer N64 (RGB modded of course) and a console to JAMMA adapter of some sort.
I'm still very grateful for Brizzo for tackling this project. I can at least test my Aleck board that came with no carts! But I think now that I've tried it, it's going back on the shelf.