Addendum to
my post above: you could even bypass the need for custom strings entirely.
Create a new attachment point at the tailpiece, get a fat off-the-shelf, long-scale B string, discard G string, move others.
As far as which B, a D'Addario .145 has about the same tension as a .045 G, scale length being equal (so if you take out the G, you can put it the B with no increase in stress for the neck), whilst a .130 B is in the ballpark of a .040 G tensionwise.
3) purchase tuners with larger holes or slots in the tuner posts;
If the string tapers down to a thin enough diameter he won't strictly
need new tuners IMO; however, proper bass tuners surely work better with bass strings.
Hofner necks are very fragile - I don't think it can handle the tension, unless they are REALLY light gauge strings. When I bought my old Hofner many years ago, the neck was warped from having some heavy gauge strings on it.
This is valid advice, but not
specifically relevant to this scenario: as I said, if the new B string hasn't got more tension than the discarded G (chances are it hasn't), and if the E, A and D are the same as before or have the same diameters, there has been
no significant increase in tension. It's not like the B will warp the neck merely by virtue of being fatter!
But yes, a thin neck probably narrows the Goldilocks zone for good tone+safe tension. I only wanted to show that, if the OP really wants to try BEAD on a Beatle bass, there are ways to circumvent difficulties and get it done without major overhauls.