If you get a 242 from an older XJ (pre-95?) you'll need to swap the input gear, tailshaft is same internal slip yoke.
The VIC gear switch on them is 2-contact, different to one on 249 case and it's not possible to swap them
cause they are different length and located in different locations.
If you get a 242 from a newer XJ, input gear and switch connectors are same, but for external slip yoke
you'd need a driveshaft from a ZJ with an ESY 242 case. Pretty hard to find.
Or just cut up your 242's output shaft to same length as 249 was and re-use the original tail shaft,
just add a rubber boot for splines from any ESY XJ tailshaft.
They're pretty much the same, ESY and ISY tailshafts, just different length.