Another option is to get a system 11B and stuff the missing sound parts in it. Then it will work for High Speed. Its not that much stuff nor anything top obsolete.
I dont have any right now, but i sold one about a year ago. So you can find one.
https://pinside.com/pinball/forum/topic/for-sale-fs-system-11-11a-11b-11c-mpu-works-100