I don't have mine accessible right now, unfortunately. But, the caps should be a standard size. I think there are ASTM standards or something like that (UPC?) which dictate the diameter, depth, tolerances, etc. for fittings like that.

Regardless, the cap could have almost zero depth to it whatsoever and it would still work- you'd just have to push the axle through a bit farther, and find a thicker spacer to stick in back. And, if you use a shallower PVC cap then you'll end up wasting less grease as well.

'87 Xtra Cab, 4wd, 22r, 5spd
'92 Xtra Cab, 4wd, 2L-TE diesel swap, 5spd
http://toyotadiesel.com/forums/showthread.php?t=2502