[R-390] Need info on R-388 collins Mechanical Filter kit

[RLucch2098 at aol.com]

Hi All;
I have what looks like an R-388 but it has NO tags & not sure if its a 51J-3?
It doesn't play except I hear the calibrator on a few bands.
Not being a tech, I was hoping it would play somewhat, hi!
I'll check the tubes next but my question really was, I noticed the front 
panel hole around the BFO control has 1/3/6 imprinted to select a Filter. The 
Knob & shaft is missing but inside I notice a box labeled Collins Mechanical 
filter kit(forgot the model numbers) with provisions for 3 plug in filters. The 3 
position has a Collins 3kcs mech. filter.
I was wondering if these are rare? Maybe the last fellow installed it wrong?
Can is be removed easily? Anyone know its value?
I am not looking to sell this unit, just asking because I never seen one 
before!
Any help will be appreciated.