The two 100u/50v capacitors on the supply rails are obviously supply decoupling capacitors, and thus shouldnt be BP types.
Replacing the 100u/6.3v capacitors in the -ve feedback path with BP's is fine, and harmless. Personally I would use 16v rated types at least.
Im really not sure whats going on with the arrangement between the + and - inputs of the STK! The effective DC blocking capacitance will be 1.5u which seems a bit low to me... I would not mess with this arrangement though as it might be important for the stability of the amplifier.