Morning mate.
To be honest, you don't really want ANY play in the uj spider bearings. If you have a little, you'll need to be driving to suit.
ie; Don't side step the clutch to launch it.
The force coming down to your diff through the prop to get it all turning will 'take up' the slack in a worn spider/bearing. If the slack is too big, and the request to turn the diff too urgent the possibility is that the shock will snap the spider rather than turning your rear wheels and moving your mini-cab forward.
Hope that helps you decide mate.

I also own a 4x4 cosworth minicab.....