The Z heads work with your choice of twin cam or single cam setup using the chain
you have a choice which is great and the provision for the chain and cogs is casted
on all the heads up to the last Z head.

Be aware not to confuse the post 2011 Z is a different engine with reversed flow and alloy block etc.
I think its ZJ which is the wrong and different head altogether.

Do you know a rough cost of the plates and bits and pieces involved? Im currently deciding which way to go as ive already got a built A15 but want to go something turbo and a bit different.

that depends on everything.

for this setup, you will need intake and exhaust manifold, head, bunch of pulleys and belts, custom head gasket and the plate.

For the original setup - not this modified version as its yet to be finalized.
To get the plate milled up in Australia - expect $600 give or take
pulleys and belts ~ $150
head 2nd hand ~ $200

after that it depends on what you want. efi or carb, turbo or not, dizzy or leccky ignition,

like anything this custom, there will be hidden costs depending on how much work you do yourself.

I reckon I'm in this for around $2500 already and I have a box of parts and a bare block on the workshop floor.

Im working towards a turbo, efi, electronic ignition setup - it would be less if you went NA carb.

I'm needing to save a few pennies myself just to buy the idlers and missing bits to get everything laid out correct.

I'm also looking at doing the timing plate with as little material waist as possible. 266.7mm x 266.7mm x 38.1mm billet blocks are a little expensive.

So far the only crucial part to the plate is the crank seal bore location and mating oil pan surface. Get all that correct and the upper half is peaches.

If the bottom sump seal section was removable you
could save alot of material all up. A step seal
like you did with the rocker cover could work.
However timwise might be a head ache for you.

For anyone looking at this twin cam setup you
must factor the best route is NA with factory
Mazda ecu and bits to save a bundle.
Otherwise if you have weber or likewise carbs
a simple manifold for the B series will also
cost the same as an A series as would any rebuild.

Mazda ecu has a way of just running ignition many
miata guys do this when going for their famous cheap
stock bottom end 160+kws atw b6 setup.
eg. head milled 2mm, cams, 45mm webers, headers and tune etc.
clutch is a must though like any high hp increase from stock.

I purchased a block of material for doing the lower pan seal and crank seal.

$30.00 just for that block.

I have some plate on hand for the upper portion

Anyone want to donate some idlers to this?

Anyone on the miata forums in the US?
Im sure plenty of b6 guys have a few
they replaced over time

Time to CNC the first part.

looking forward to see the changes made and how it all works out with the two part design you have in mind