try railway track iron steel.They don't explode and retain heat well

Yeah snag some nice round river stones, just take walks along a creek with a backpack, wont take too many walks to get enough :) make sure they haven't been in sea water cause those ones like to explode.

head down the bay of plenty for old railway lines round whakatane,kawerau they not doing anything any more

The old brake shoes off railway carriages work well, and they even have holes in them for lifting them out of the fire. I have also seen short lengths of heavy chain used, though I imagine they would cool down very quick.

More than likely, all out maunu and kamo too

a lot were built for aesthetics though

Rivers stones at the landscape yard,most come from way down Sth now ,get some bigones in the mix just hand select them

That is a hogget in the pic... Sons engagement party.....
The last one was a couple months back an annual event the Car club annual mid winter xmas party.
Total costs for 40 ppl.. including home made roast spuds kumura, pumkin, galic... peas carrots broccolli and deseart  home made apple crumble pie  cream and ice cream   $370
That included everything down to the marinate and wood.
We use proper plates knives forks.. more civilised and at the end of the day less work mess ...except for desert.
And still left overs for ppl to take home
Labour:
Basically its one person on the spit, the Wife and one of the wives do the kitchen and husband helps clean up tidy the shed, quick sweep around with the petrol water blaster.

Also the spit gives 'atmosphere'  and there 2x 12 gal drum 1/2s are split , used as camp fires for the evening....

A hangi has a lot more work and a lot more ppl ....and bigger clean up.

Just a few experienced observations from over the yrs.

The joiners that bolt between the rail lines are what u are looking for....the bolt holes makes thenm easy to 'handle' drag out .. and hold the heat better than river rocks

And I repeat.. caution using 'un cured' 'virgin' rocks... they tend to explode unexpectadly....so I strongly suggest  pre fire them well before the day.... a hole in the ground, small tunnel, a vaccuum cleaner that has a blow function, and deseil dripping from a pipe does the trick very well.....and get that right, along with a few manuka logs on the day .....makes an impressive heat source without taint....get it wrong  ......

All of the above is from 40yrs of personal hand on experience.

mowerman wrote: try railway track iron steel.They don't explode and retain heat well

Yep. That is what my in laws Use. Chopped up railway iron.