Hi, Use OPA604AP to replace I/V convertor, AD845JN to replace output buffers (the two nearest the sockets). The offset null pot is not configured correctly to work with the OPA604s or you could use these all round (you would need to reconnect the wiper of the pot to the negative rail rather than the positive as now). I would not recommend changing any caps at the moment, try the opamps first, and be careful unsoldering parts as I said earlier. It looks easy, but unless you are use to working on double sided boards, those plated through "vias" will cause difficulties. You can bypass the electroylitics as you say, I replaced all mine with low "ESR" types (Panasonic and Elna) and bypassed each one underneath with a 0.1mfd surface mount cap which fits perfectly the 5mm lead pitch. The Op-Amps run in class A anyway for all small signal conditions, and adding a resistor or current sink/source will just increase dissipation as the Op-Amp is forced to counter the extra load. Sorry, I know some will disagree on this point ! Anyway above all ENJOY and do let us know how you get on with this.
Karl