So I am getting the Maddat tunnel installed by my mate who is a fabricator/welder. Any tips and tricks i can let him know for engineering purposes and ease of fitment? I do recall 10mm overlap all the way round?

Thanks

I thought was 20mm overlap all round?
My guy also said use mastic or some crap.

Also mad dat tunnel doesn't allow stock heater to fit. Make sure you work that out. Possibly why pig dog loves his 120y tunnel more than the 180b and stanza ones

yeah i was told 20mm overlap also, welded on both sides

and yes i am a fan of the 120y, and any other standard datsun tunnel, as they look a lot neater in my opinion than a maddat tunnel. and also allow plenty of room for the gearbox and the standard heater to be retained if you do it properly

is it big enough?

The 120Y tunnel came stock with a 71-series transmission. So it is big enough.

The 1976-1978 tunnel opening has all large opening
The 1974-1975 tunnel opening for auto large opening
The 1974-1975 tunnel opening for manual has smaller opening

yeah i can fit my arm around the gearbox in my car. engine is mounted pretty low so gives even more room.
but they are the same size as a 180b or 200b tunnel. obviously a little less room in them than there is in a 180b or 200b as the engine is usually mounted further back in a 1200 than what a standard car would be.....but still lots of room