Thats a very old fella, new ones have a different back plate so no stright swaps Im afraid, not a big deal though, sounds like you have a gravity HW system so new one will have to be set to gravity
Electrically not difficult- yon street light time clock will have a live and a neutral to make the innards go round and round and (usually) a great big internal microswitch which is volt free.
Electrically you can replace it with any single channel controller/programmer, mechanically you will have some making good to do. As long is the thing isn't an integral part of the boiler then you are permitted to DIY it provided you can do the job competently- safe use of a multimeter measuring 240v will be adequate.
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