Oven depth for built in fan oven

Hi all, I’m having a problem finding an oven to fit into the recess of my old oven, the old oven was a diplomat (which you can’t buy any more) with a recess depth of 496mm but having changed the element & thermostat & finding the food was still burning my wife decided she wants a new oven, apart from the depth problem I also have an electric junction box at the back of the recess (don’t know what for, it’s one of those with a blank plate on the front, there is also a gas pipe leading up to the hob by the back wall. We have bought a new oven but it protrudes from the unit slightly but it is also up against the junction box & very close to the gas pipes at the back of the recess, I can put a couple of battens round the front of our units to get the oven fitted which, though not ideal, would not look too bad but I would like to know if there is a safe distance for the back of the oven to be away from the junction box & gas pipes.

Many thanks to anyone who can help.