Z25 is pretty close to a 24' black widow hull bottom and weight. I had a 24 widow and so did fishnsucks. Figure a 454 with 365hp is a 60mph boat. Need about 500hp to go 70mph. Assumes the correct diameter size/pitch prop of course. Chevy 454 marine engines seem to be very plentyful so I would go that route. I see a couple late 80's Z25 boats for sale in MN, WI, and OH area from time to time. All freshwater boat histories and an inexpensive way to get into a Donzi. They are well built nice boats. Most are kinda rough shape after all the years however. Nothing that 5-10 grand worth of TLC wont fix however.
Tuco: When you have to shoot, shoot, don't talk.