I think you have the connector J8 right. First four pins are one side of GI, white with striped colors. The last four is the other side of GI and solid colors. It should not be that critical the order as long as they are grouped up properly. The manual should have a wiring diagram page with colors.

Isn't that board missing the F7 GI fuse? I thought they had a 20a GI fuse on the power board in system 7. They did jumper it out in later system 11 when they fused each individual GI string after it leaves the power board. I would make sure you have a fuse(s) somewhere in the GI circuit. Since that board does not have a F7 GI fuse on the power board each string should get one 5a fuse after it leaves j8.
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If there is no fuse in the GI anywhere you must add them. Best bet would be to fuse each string with 5a after it leaves the power board in your case. WMS moved this fuse around from before the power board, on the power board, then after power board. But for at least some games I am pretty sure the GI fuse goes at F7 the power board. They say transformers never fail, well, a short at a lamp socket and no fuse is a way to smoke one.

LM2679 is great voltage regulator part and my go to. Just too bad they cost like $6. The datasheet even has a cook book circuit.

I will probably not do this power supply. I actually canceled my WMS 3-6 power supply because I did not want to price compete with others and just did not seem worth the time. Right now focusing on stuff I can easily do with automated surface mount assembly.

Your picture I think confirms cosmic gunfight GI fuse should be on the power board at F7. That board should be marketed as system 11 compatible only (maybe 9?) until the fuse is added. Someone is going to melt a transformer.