You can find Test sets schematics at artekmanuals, inside Hewlett Packard 8510A Operating, Service-V5 file, which contains schematics for testsets (but only for "A" versions of 8511-8515).
Also, you can download 8517 service manual from Keysight (without schematics, but with part list and block diagrams)
As I see, control board for 8511 and 8517 is a same, but you need 08513-60011 or 08517-60001 Attenuator|switch driver (not shure, which one).