Try Mr. Cool
I purchased risers, elbows, and hardware for my 350Q from them.
I'd also check with Paul here: http://www.marinemanifoldcorp.com/
You can also try "1800runsnew".
Thanks for the suggestions!
The Chris-Craft Marine Power 454 manuals are in the club library but you have to search for them as if I recall correctly they are mislabeled in the file description (they may say Crusader). The manuals have parts listings and diagrams illustrating the flow of coolant and raw water through the cooling systems.
I have closed cooled 1981 454s and the setup is fantastic as the entire integrated manifold-riser assembly is part of the closed cooled circuit with the raw water injection piece being a small cast section at the end. I don't have great photos of the manifolds plumbing but you can see the brass 45 degree elbow fitting where the raw water is injected in the attached photo. I do have a photo of the heat exchanger/expansion tank assembly and the mounting brackets off the aft end of the engine.
Best of luck!
Buy raw water cooling kits from Marysville Marine Distributors, a Crusader Marine distributor.https://www.marysvillemarine.com/parts-diagrams/crusader-marine
Find the application you want, for instance a front mounted heat exchanger kit:
The kit part numbers are shown, email or call.
I converted a pair of Mercury Marine 454's several years ago, easy job, worth the money, lot of benefits to closed cooling even in fresh water.
You should able to buy the parts from Marine Power Inc.
Marysville Marine is also a distributor for Marine Power. They are the best source for advice on installing a raw water kit. The link to the Crusader parts view is to show the components of a closed coolant system kit for a 454.