I think you will be sorely disappointed if you do all the work to install extractors "under cover" and don't do any upgrades to compression, camshaft, carburetors, ignition timing, head work, etc, etc and then expect some miraculous results to "get some performance" with a "sports tune"..... The standard L-series Nissan exhaust manifold is a pretty good design as is and, in combination with everything else staying relatively standard(ish) I think the best short term solution to consider would be to increase the diameter of the exhaust from the manifold to at least 2.25" or 2.5" throughout the system. I would then concentrate on getting every other system dialed in as best it can be to restore performance at least to factory specs (perhaps beyond with better fuels we have available now) while you plan next upgrades. This would provide a good basis for an upgrade to the engine (carbs, cam, headers, etc) down the track and then you'll also already have a good exhaust set up in the car that can be used, too.
Hey Pista_510, yes I agree, my mechanic wants me to get the extractors first but I as well don't see the full benefit for this right now, yes it may be an easy gain in power but a waste if not done with other upgrades as you mentioned.
I was only going to do a 2" exhaust with hot dog and hi flow mufflers and then some smaller upgrades
like hotter plug, timing and valve adjustment and a upgraded coil/leads and air filter and a good tune
the car runs real nice as it is and am just looking for some more response at this stage, a bit more noise would be nice as well and accept that unless big mods are done there will not be a huge gain in horse power
thanks for your feedback