From the VAX APL Users Guide page 1-3 comes an image of the LK201-EC variant with APL keycaps:
With this image as a reference I designed a set of replacement keycaps for an existing LK201 using the Open Office Drawing tool (source file) and the excellent Simpl APL Unicode Font:
These were printed out using a laser printer on the self-adhesive transparency paper provided as part of the Hooleon Keyboard Sticker Label Making Kit. These were then cut out using a scalpel and mounted on backing stickers which are opaque. A final top sticker adds a textured finish and protects the printed label.This is the resulting keyboard:
Left Hand Side:
Right Hand Side:
I've also uploaded a short video to YouTube demonstrating how you interact with VAX APL V4.0 using this keyboard together with a VT320 terminal.