V8 camshaft retaining plate?

I've just got a new camshaft for the 3.9i I'm rebuilding for the 110.
It's one with the step machined into the end by the timing gears to
allow it to work with the retaining plate fitted to the later engines.
I know the interim engines (gear driven oil pump and dizzy) had a full-
circular retaining plate and then on the 4.0 and 4.6 LR moved to a
semi-circular plate. Does anyone know if the critical dimensions are
the same for both types of plate (i.e. will either work with my cam)?
The semi-circular ones seem easy enough to get hold-off, the interim
ones less so - in-fact I can't even find a part number for them.

I'm assuming it's a good idea to fit one - it's just a case of
drilling and tapping a couple of holes in the block (avoiding oil
ways) and I know the original method of location, relying on a taper
on the cams reacting against the lifters, isn't considered a
particularly great bit of engineering.

Cheers,

Andy.