The 430 is an MEL engine... that is, Mercury Edsel Lincoln division of Ford Motor company. It was introduced in 1958, and with a marauder tripower option, was the first production V8 to hit 400 horsepower. It was raced by Ford in 1958 and 1959 in Tbirds, and almost won the first Daytona 500 in a Tbird driven by Johnny Beauchamp. It is rumoured that the first Bertram to win the Miami to Nassau race in 1960 was powered with 430's. The 430 was offered as a powerplant in many of the Chris Craft cruiser line to over 50 feet. The first 430's, as stated, were generators, and had a single double impeller waterpump from Sherwood. The later 431 had two pumps, the second one for circulating. The large journals on the mains and rod bearings tended to generate more heat, and CC had some cooling issues in the early version in the larger boats. There are other differences between the motors, including intake runner size, piston design and compression, and some minor head changes. While a low rpm engine, the 430 has a very flat torque curve from 2000 to 4000 and produces immense torque figures at low rpm. The HR25 refers to the hydraulic reverse and 2.5 to 1 reduction gear. Marine gaskets are no longer made for the 430, and neither are north American oversize bearings. You can get Chinese replacements. Dave Van Ness at Van Ness engineering in New Jersey has rebuilt a few of these engines, and has the hard to find gaskets. There are a big list of subtleties in the 430 that would slip by a lot of engine builders. They are a very tough engine, and properly applied and cooled are hard to kill. The big issue is cost of rebuild. The combustion chamber is in the cylinder, not in the head, and the deck is surface 10 degrees to the bore, like a 409 Chevrolet.
The 431 and 430 used solid lifters. The valve lash is .025 hot, and .027 cold. You wont find the stepped pistons anymore if you rebuild, unless you order custom forgings.
I have a 1965 21 foot Superport that came with a 430 originally. If you want a significant database of info on these engines... go here ford-MEL-engine.com. I post there under Chris Craft Crazy.