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Let me understand, ..... the tuner plumbed the vacuum line to the distributor straight into the inlet manifold so that the distributor will see full manifold vacuum at idle & therefore will have full vacuum advance, ..... while idling. Right?

Well there goes your 5 degrees of initial advance straight out the window.

It would seem that the tuner has fallen for that old trap of assuming that he knows what he is doing & those clever little Datsun engineers were complete & utter morons when they designed that "ported vacuum" fitting on the carburettor.
He got that one back to front.

This fitting allows the distributor to see manifold vacuum at all times except when the throttle plate is closed. At engine idle the distributor bobweights have been returned to the 'no advance' position by their springs & the vacuum diaphragm has no vacuum signal so it too is in the 'no advance' position & that's when you get your initial advance of 5 degrees.

Perhaps your tuner had better learn how to read a workshop manual.

Yes 5 BTDC is the factory setting for north american models.

More than that it may ping, especially if it doesn't have the correct auto tranmission distributor. The vacuum advance and mechanical advance is special for it.

No dyno 'figures' as of yet.. it's all tuned fairly nicely, but still trying to sort out some niggles with the timing/fuel and the auto.
Somethings not right with the timing.. my tuner has had to set it at 5 BTDC for it not to ping and then plumb the vac advance straight into the manifold so it advances faster (kind of a half-ass stop-gap measure really) Not too sure what's causing it either, but its running at least. PIA really but hopefully I'll get it sorted

Awsome! and the dyno results?

Thanks guys, all sorted I think
I made up a new oil pump gasket out of some thick gasket paper and put a bit of silastic on there as well. Seemed to fix it ..and yep, the oil pressure switch fitting was weeping a bit so whacked some teflon tape on

Its the small, simple things that you wouldnt expect isnt it?

Yeah, It might seem inprobable but mine kept leaking ever so slightly and that was it.

The best place to get that stuff is a hardware store or plumber... :)

and put some tefflon tape on the thred for the oil presure switch.

Check if the filter has the O-ring on top of it? The mating surface may be uneven too...