MA Slap Bass overdrive question

[rubyrudy]

Hello everyone! I am new to this forum, so please sorry if I have chosen the wrong place to post this topic.

My soldering skills are very limited. I have only made few pedals from kits and fixed some stuff.

Today I have decided to change the loose jacks in my old Slap Bass overdrive. To my surprise I have figured out that there is a room for some more comments, including switches, at least three of them.

I have tried to figure out the circuit type as I am supposing that it is a copy of some famous effect. But unfortunately I failed due to my poor electronics experience.

Maybe someone can have a look and point me out what type of circuit it is, so I can try adding missing components.

I also found out that even that the metal casing has holes cut for those switches, only they are covered with front labeling.

Here are some pics. If you need anything more I will gladly provide any info needed