Technical Aluminum timing cover on 322 nailhead

Hi.
I tried to ask this question on the nailhead forum, and also e-mailed centerville with no reply, So now I'm here.

I read on the centerville webpage about using the later nailheads aluminum timing cover on the older engines, and that this would require the use of the 1956 322 waterpump .
Is this because of hose placement or something else? In my hot rod that's not of much interest and I would rather update to a later aluminum pump while at it.
Does one use the 322 or later fuel pump when doing this change?

 

No help but a bump for them that knows.