After ohming the windings out, I'd place 6.3 AC from a small fil. xformer across the primary in two variations and start measuring and plotting / sketching what I see on various combinations of the secondary. -- Fun.
Also see if any of the windings are internally connected to the case. May be critical if contemplating a potential HV bridge circuit.
Oh and bake it in mummy's oven at about 140F with the racks out and a piece of plywood under it to protect oven floor for several hours before applying full voltage. Wait till mums goes to see a sister, etc. for a whole day or so.
. Turn on kitchen fan too.