Being a bit of a TA-4 buff, I'd have to say your float TA-4 is a cool idea
, a great bit of original thought and Whiffery :)
From what I can see in your pics (a side and bottom view would've been helpful) the problem is there just isn't any structure where you've picked to attach to the fuselage on your model. The front attachment is in a void called the 'Forward Hell Hole' that gives access to aileron power pack, engine intake, front face of the engine and the CSD unit, also a rack can be attached here for a large bag (for pilot kit).
The aft attachment you've chosen appears to also be in a void, called the 'Aft Hell Hole' where we gain access to the single point refuelling receptacle, hydraulic couplings, drains, the rear engine mount, wing tank fuel pump and the jet pipe attachment fitting, it would severely interfere with engine changes (the whole tail comes off an A-4/TA-4 to effect an engine change) and make it unnecessarily complicated.
The best attachment option would be to use stores station 3 on the centre line belly where it is already stressed for 3600lb (?) weapons carriage. The loss of this weapons station would not be a big problem as you could install a fuel tank in the float and instantly increase the jet's range. Also a single pylon attachment would reduce form drag and limit the affect on the jets manoeuvrability requiring no modification to do engine changes or standard A-4/TA-4 maintenance. Also you could use the now unused main landing gear bays as extra fuel tanks for even more range.
Are your out rigger floats fitted to the outer weapon stations? These stations are cleared to carry 500lbs each and would make an excellent place to fit floats with some beefing up of the structure. There is a bit of a prob with outriggers that cannot fold or retract as an A-4 can roll at approx. 720deg a second, pilots that do this with a full wing tank have actually blown out the tip of the wing tanks due to excessive G at these locations, so one would think a non-retractable/foldable float assembly wound not fare well either.
I'd be concerned at the amount of spray that the voracious J-52 would suck up at full power, so it makes sense to increase the width and length fore and aft of the gun blast strakes and have them double as intake spray guards without affecting the guns.
Well done again, hope this helps,
Neil