I did some testing last Saturday and the results up 'till now look very promising.

There was just one problem as in that I couldn't test it during a pull. In my haste to get everything ready on time, I forgot to include some sort of means to block the compression screw (on my earlier head I did do this, but for some reason I didn't have to use it, the screw just staid put)

So, using an Allen key to keep the compression set, I ran the engine through a couple of tanks, both at idle and whilst revving it. I adjusted the idle and the high speed needle so that the engine ran as lean as possible and set the compression as low as possible without the engine quitting.

The engine ran much cooler. Just waiting for 20 or 30 seconds after shutting it down was enough to let it cool down to a temperature where I was able to not only touch the head, but to put my hand on it and hold it there comfortably (and that's with the tractor standing still, without any forced cooling whatsoever!)

So, the only ting left to be done is to provide some way of blocking the compression screw and then try again. Our next pull will be in two weeks, so I'll see what happens then!

Finally, I just want to say thank you to everybody who contributed to this thread. You were all a great help!