I thought a lot about it  and I decided to not drill 
1.25 inch hole in the pump and insert a tube. I was worried that 
the drill might hang up and destroy the pump housing. 

The area of the outlet port in the block is about 3.25 square inches.
The area of a 1.25 OD tube with a one inch ID is only .78 square
so the one inch tube is a large restriction in the flow.

So is the stock housing for that matter. The area of the water
outlet passage just below the upper most bolt boss is 
even worse at about .66 square inches. IMHO this is one of the major reasons
why the Mazda pump cavitates at only 8000 RPM and flows so little
water when it is not cavitating. See the picture below of the pump with
the upper part cut off and the water passages ported as much as possible. 

It makes no sense to have a hole in the block with 3.25 square inches
and then have a restriction in the pump of .66 square inches.

The lower passage is the by pass and is way too large IMHO. That
internal volume of the pump could be put to better use as outlet
passage area. IMHO Mazda really screwed up when designing this pump.
One major problem is the partition between water outlet passage and
bypass passage is simply in the wrong place.

Jeff said the big problem is the pump housing has too low of a profile 
and I most heartily agree. The pump housing would be much better if 
it were 2.75 inches thick rather than 2.3 inches thick as it is now.

A lot of the sins of this pump could be fixed with a thicker housing
but as I have said on here before engine length is everything to a car
stylist.

Be all that as it may I am now working on plan D which is a compromise
between an all new housing and inserting a tube.

I think I am going to do open heart surgery by cutting off the back
wall of the pump and removing the existing partition between the water outlet
passage and the bypass passage and relocating a new partition further
down in the pump housing. Trying to operate on the partition through 
the holes you see here is like doing brain surgery through the ear canal.

The final outlet tube will be 1.5 inch OD with an 1/8 wall and a 1.25 ID
or about 1.25 square inches which is standard for most rad plumbing.
Twice the area of the restricted stock pump. Incidentally that is the same
size as the current inlet tube.
  
Paul Lamar
 
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