Hi John, yes, the works did make modifications to fit a J2 body on a L2 chassis with 12 inch brakes. Attached a picture of a original inner wheel arch from my L2 2036, made may 1933. As you can see the modification the works did, just shape a bulge with a hammer/mallet not more it is very differet to inner wheel arches of P-Type - such as Steve Gilbert make today.
On the other pictures you see the inner wheel arch still fitted in a original L2 body.