To do a good job of it, you really need to remove the adaptor in the head and that is not something I'd like to try to remove without taking the head off. If you only doing hoses, then leave it at that. If you ever take your head off, blank it then.

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If I just want to replace the piece of hose, not blank it off, should I still do it with the head off?

No, just take the water pump off.

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this is why the hose is flexible, so that you can squash it to fit between the two pipes. Putting radiator hose in instead is difficult to do without taking the head off. So next time you take your head off, make a decision, blank it off, or put stronger hose on.

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Aussie Leyland, Aussie Factory, Aussie Mini S.

if you look at the photo of mine, the blanking plug is just an allen key (socket) head bolt. The thread in the head is 5/8 UNF, so getting the bolt is easy. The allen key socket is 1/2", so all I did was screw a nut onto a 1/2" bolt, put the head of the bolt into the socket and screw it in. There's a rubber washer thing (has a funny name I forget) under it, and I might have put some loctite on it

with the water pump I just tapped a 5/16" UNF thread into it, and screwed in a bolt with the head cut off and flats filed on either side

can you by a suitable water pump without the vertical outlet on it. or do they all have it.

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Aussie Leyland, Aussie Factory, Aussie Mini S.

You can buy pumps with the bypass undrilled

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Too many cars, and too little time.

Once upon a time in my adolescent past, I had a by-pass hose let go, while in the bush, miles from anywhere. I didn't have a spare, do had to use heater hose. I also didn't have a spare water pump gasket, so had to fit the heater hose without removing the water pump.

What should have been about a 20 min job - including removing and refitting the water pump and the radiator, ended up being a monumental struggle that lasted for close to an hour. First try the hose fit nicely, but I had cut it too short, so it didn't seal properly. Then I spent ages trying to fit one that turned out to be a little bit too long, then I finally got it right. The joys of ad-hoc bush repairs without the right tools or spares.

The upshot from that was that I have NEVER had a by-pass hose on any of my engines, and it has never been a problem.

The only issue that has resulted from it was trouble getting the water temp up to normal when in the Blue Mountains in the middle of winter, but there are easy remedies for that too - like a bit of cardboard across the grille.

I always have just two small holes drilled in the thermostat. I know some people who remove the thermostat altogether, but they live in hot climates and I'm told it is not advisable.

Hope this helps.

Cheers,
Watto.