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For all practical intents & purposes, the A15 is nothing more than an A14 with 5mm more stroke, so a head & cam change will not produce any real benefits by themselves.
If you have a water heated inlet manifold, then you can switch to exhaust extractors without any negative effects.

Webers [plural] on your engine would be the biggest step backward you could take, however a low cost adapter & a single twin barrel downdraught Weber from any one of a number of cars will add a nice measure of pickup & pep to an otherwise stock engine.

The thermo fan is another myth too in my view. It requires electrical power to run it & this drain imposes additional load on the alternator which in turn sucks the additional power from the engine. A stock fan has some of the load lifted from it when you're driving by virtue of the windmill effect when the air is pushed onto it through the radiator as a result of the forward movement of the vehicle.
If you have overheating problems, then fix the 'cause' of the problem first before adding additional fan capacity.

Again, in a near stock application, the stock fan will be fine. Your money would be better spent on a Pertronix electronic conversion ffor the ignition. These are basicsally a points replacement system but provide a more reliable spark.
I run platinum plugs in mine & these require a lower voltage to fire across a given gap at a given compression pressure. Combined with the GT40R coil, & silicon plug leads, I get every cylinder firing every time, no matter what the load or engine speed.

You will probably need st spend a quid to ensure that the carb is correctly tuned to your engine.

Make sure that all the factory tune up specs are right on the money & that little car of yours will scoot right along, but it will be right thrifty about it at the same time, particularly with fuel at more than $1.50/Litre.

The longer stroke of the A14 will give you a nice boost in torque & the single Weber, when correctly tuned, will help maintain a good vacuum signal, which is what your auto trans wants to see as it relies on the vacuum signal to help with the shift points. Bad vacuum & the shift points will be higher. This becomes a drag pretty quickly in a streeter & is why twin sidedraughts [which will have almost no vacuum] are so bad.

Stick some tidy but low cost 13" wheels on it & run 185x60x13 on the front & 205x60x13 on the rear & you get a nice bit of rubber 'rake' with an agressive stance at an affordable price.