You would be best asking "how much power do I want" ?
The x flow is an absolutely excellent engine for tuning, a bit old in design but can and does produce the power when modded.
As yours is a 1600GT engine it will be MK1 mexico spec cam wise, ie 84 bhp so is a good start, it is a very good tractable cam and what I used to run in my tuned auto's.
Headwork is extrememly efective on these engines, then a 32/36 webber carburettor, fits straight onto your manifold as you should have a twin choke on there anyway.
Fit a decent K&N air filter(element) in the air box, decent exhaust as well.
Next with the dizzy the advance retard curve can be altered by trial and error, by pegging back the advance stops inside the dizzy so it runs MUCH more advance low down(with ported head), but no more in total.
From memory I used to get around 115 bhp, with this, although mine was auto it would leave for dead a 2.0 pinto injection manual, as it did my friends of the time!!
Of course you can go a lot wilder with twin 40/45's, and a much better(electronic) ignition system, or even to different engine in the long run such as pinto, the x low is a compact engine but someof the jap stuff is smaller and a lot more powerful.
tabetha