Would this immersion heater fit my tank? (Photos to show)

Now just to be awkward there is another option. The Willis Heater

https://mybuildingsupplies.ie/shop/plumbing-heating/water-heaters/willis-heater/

Its been discussed before here and is an ideal way of getting the maximum amount of heat into your tank.

Previous discussion

where is the thermostat located on the longer immersion element? As if it’s not sitting any lower than the existing stat, it will still trigger ‘max temp reached’ at the same time (and with the same amount of water heated) as the older element.

I’m not so sure a longer element will heat more water…. Just heat the same amount of water faster…..

I toyed with the idea of a longer immersion element before, and was told it would be fairly pointless, and if I wanted to heat a larger volume of water a Willis was the only way to go….

Of course a longer element will heat a greater vol of water than a short(er) one, thats how the dual element immersion works, as pointed out though, the problem is the stat, both its length, which may be less than 1/2 the element length and its top mouning, while you won't have to use ~1/2 the fully heated vol, cold incoming water will have to rise up a fair height before the average temperature of the stat falls to the stat cut in point, dual element immersions are far "worse", if you heat the "sink" portion to its cut out point, then no more heating if you change over to the "bath" until you use up maybe 15 or 20L of water. I don't know why one can't buy a single element immersion with a equal length stat which would certainly mean cylinder heating occurs far sooner. A destratification circulating pump would do the job but at greater expense. What is the cylinder volume?.