Hello Tim,
When Oliver Archut was still alive, there could have been a solution: he could have would you a Hiller T14 copy, which is a bit bigger and fits the space of the old 2148 transformer better. But that is no longer an option.
There is no need to drill or otherwise permanently deface your mic. Just in case one day you find an original or copy of the large Hiller T14 or Henry Radio 2148 transformers, or in the meantime, to mount your T14/1, you can conveniently glue the transformer into the existing space with E6000. This revolutionary adhesive conveniently does not mar, deface or melt any parts, and, if you need to remove the transformer, the transparent glue peels off in one piece, leaving no residue.
At least that is what I would do.