Question for engine builders among you?

[Rubberdubber]

This is a Non-Audi question but probably relevant to Audis as well.
We have a Japanese Import van (Diesel) which has been experiencing a lot of overheating issues of late. I exhausted my own limited engine building experience (Lol) a long time ago and the car is now in the Garage. It has turned out to be a Head problem and we have had it pressure tested and it failed, so a new head is the only option.
Prior to that we thought the head gasket was possibly the issue and my mechanic says it looks like someone has fitted the wrong gasket in the past, so it still may be the root of the issues. There are 4 (4 Cyl engine) water jackets, one per cylinder, blocked off by the gasket. He is trying to get a better gasket, apparently there are 4 listed for the engine but he says even if this is not possible he is tempted to drill out the new gasket to allow better flow of coolant.
I have to say, again in my limited experience I am tempted to agree with him and it certainly sees to make sense in relation to all the air-locking issues I had and failed attempts to bleed the blo**dy thing. Can anyone advise if this has any downsides?
Appreciate any advice anyone can offer, Thanks.

[squarebare]

Is the engine a toyota 1kzte?

[Error404]

Why not just fit the correct head gasket?
You can easily mess up the coolant flow and cause hotspot problems by modifying the gasket - the orifice sizes should be arranged to ideally balance the heat transfer across the cylinders and around the combustion chambers and exhaust valve seats.

[squarebare]

The problem with the diesel is, the 4 different gaskets may only refer to the thickness to obtain the correct compression, the 1kzte diesel also had 2 different heads with different valve lenghts and they're overheating is well documented as they run retarded injection to combat nox emissions for japan, unlike a petrol if they run rich they suffer from overheating. The make of vehicle would help here.

[Rubberdubber]

Apologies, I was just thinking it's general engine question, it's a Mazda 2.5 TD, WL engine from 1996. All 4 gaskets came in and these holes were blocked on them all, so we decided they must be meant to be and so they (manufacturers) are likely know better than us. So it's built back up and running, no issues so far so fingers crossed. Thanks for he replies