However, the cost of a 50mm coupling is not too bad.

GBP 19.99 Approximately US $31.35
Shipping: GBP 12.00(approx. US $18.82)

My $0.02 is to go with 2".

Do so with care. My club has a trailer for our L23 which will not accept
a 2 inch ball - it must be 50mm. For some trailers, that .8mm difference
makes a difference (pun intended :-) ).

Tony