Bdevlin -
Call Danny at Grady customer service- he can e-mail you their specs for your boat, including the placement of thru-hulls and the grady PN and corresponding attwood or perko or whatever part number.
Grady customer service is absolutely fabulous....even to owners of old boats...
He just did this for me on my '97 voyager
However, you should note that just because it is what was speced out, does not mean that is what is on your boat.....
As for plastic scuppers and thru-hulls, I think it really depends on where you are as to whether you want to spend the extra money on stainless or bronze. Perko and Attwood make stainless and/or bronze that will work just fine....but the price is around $30 per thru-hull vs. $6.00 per thru hull.
Here in the PAC NW, we have boats with plastic thru hulls where the thru hulls last longer than the motors....but that is because we really do not have a UV issue up here

. To the contrary, southern cali or southeast boats get a ton of UV damage and plastic thru-hulls deteriorate pretty quickly.
No question, stainless are better....