O2 help with bass boost and 1/4 jack mods

Hello everyone. This is my first post and i did some research before posting but i couldn't find a direct answer to my question.
I plan on building an O2 or at least ordering the parts in the next week.
I did want to make two mods to the amp. I would like to add a 1/4 jack and bass boost switch.
From what i have read the smaller enclosure is to small for the 1/4 jack but i found this O2 for sale which has a smaller enclosure and a 1/4 jack in the back.
O2 amplifier (bamboo faceplate)
This is a link to the O2 i found. I messaged him and he told me it has batteries in it but he didn't give me a lot of information i was looking for.
I would really like to know what part number i should use for the 1/4 in a smaller enclosure (should i use the same on that is listed in googledocs part list? or will that be too big?)

Also on this forum i read about the bass boost on the O2 with a 3db gain on the lows. At what frequency does this gain come in?
I am an EE student and i know i could change the gain with a resistor and cap but if i wanted to get a 9db bass boost gain what would you suggest i use?
i know a pot would be too big for the small enclosure so could i some how add the switch for bassboost again? so i would have two switches one for 3db bass boost and with both on giving a 9db bass boost?
We will not cover op-amps for an other two weeks and when this semester is over i still dont think i would be confident in ordering parts and doing this with out some help!

I don't have the O2 enclosure yet or parts because these mods are somewhat important and i want to be sure before i order. the bad thing is with out the parts i dont know how any of these things will fit!

thank you for your help! :)