This requires the minimal possible manual changes to have a stone furnace layout that you can in-place just plop down electric furnaces and eventually just have the same spacing for beaconed. You do have to move the output belt eventually for beaconing, but by then you are getting bots and that's easier.
The main trick is that long inserters can be positioned one out from the furnace so that they are out of the way of the electric furnaces. I prefer using them for the output that way it's easier to upgrade the input to fast for steel.
You can use separate input lines if you prefer, you'll just have the extra long inserters to cleanup if you care, and another belt you have to delete.
The pole spacing is done in a way that uses twice as many at first, but doesn't need deleting or moving later.