Ok nevermind that last comment about the breakable tabs. Your speakers have thebreakable tab but are postioned in the 4 hole pattern thus needing the adaptor plate to correct the mounting hole situation. I was excited to see that these Alpines might fit the space because it has an option to...
Sorry to bring up an old topic but do you have 3d print files that you can share? I am working on something similar with Alpine - S2-S-40S that have a similar configuration for mounting. Curious, these 4 inch speakers that you have the breakable tab for you to make them the 3 hole BMW mount...