Quote: A worked GX head is not the sort of thing that one normally associates with the word 'economy'
Like I said, you need to figure out just what you want, just what kind of fuel consumption is regarded as 'economical' by you, & how much performance is regarded as a minimum. Once you get it clear just what you want, you can move forward.

Just remember that new car engines have things like, four valves per cylinder, dual overhead cams, variable cam timing, EFI, & computers that are trying to 'tune' the engine while it's driving. If we could engineer all these things into a 1200 engine, we could very likely duplicate the performance of a new car engine.
What we are working with is a technological Dinosour, yet a very loveable one. We can only do the best we can with what we have to work with.

My big bore 1200 GX & five speed in my 1000 sedan gave quite 'spirited' performance, enough to impress a few unbelievers in its day, yet when driven for economy, it returned better than 50 mpg, Ummmmm, thats 17.7777 kpl or five point six two five litres per hundred kilometers.

This was with a mild cam & an otherwise stock GX engine but with a 76.5mm bore size. [1286cc]

If you want to run a bigger engine, with more power, then you can still get good mileage, just not quite as good, & probably not as often. [Then again, with the right gearing,...]

Do you have an aftermarket manifold with twin SU's or a GX manifold with twin GX Hitachi's?

Oh yeah, what do you bore out in an A14 to make it suit an A15 crank?

Quote: YOU LIE, ... you're not sorry at all.