Okay so dimensions are now sorted. I need to get thte through transom seal rings, drill the transom holes out, get the old pipes cut to fit and mount it all up. Should be easy!!

Time to call CP for bits and peices...

I'm going to plumb the water lines to the header distribution tubes with AN fittings, is -10 AN suitable? or should I just put a barbed connector fitting in there?

Also, with this set up (no circ pump) will I potentially have water pressure issues and if so, is the best place to plumb in a release dum at the back of the inlet manifold from the two ports there?

Okay, tails are in at the stainless shop getting cut to size.
I've opted to simply have a section taken out of the down leg on the tails to fit thus leaving the angles down and out the same (hopefully). This will leave me with enough room for the slip in mufflers (GGB 8" silencers in the 11" lower sections).

I'm going to wait till I get the tails back till I cut the holes in the transom out to fit. That way, if they're a mil or two off one way or the other, I can still cut the hole snug to fit better without butchering it too badly.

If the OD is 4.5", what is the best size hole to cut fot it? snug fit or loose?

I picked up the newly cut to fit tails from the shop today. They look good. Had to cut the jacket back a bit either side of the inner so they could weld up the inner tube first, then they collared the outer tube and welded it.

Still waiting on some advise about how big the through transom hole should be...

Hopefully I can get this all fit up!

Here's where I'm planning on taking the material out to fit and a shot of the modified tails.

Any advice on hole size would be great.