this is going to be a little harsh. It sounds to me like your mind is made up, and you really do not want others opinions, or good advise. You are looking for somebody to confirm your not very good idea. A merc in line six weighs about 310 pounds, with power trim. That is 620 pounds of engines on the back of the boat. With optis, you are putting 862 pounds on the back, and with Verados. over a thousand pounds. That is a lot more than 620 pounds. But it is your boat. You can do what you want.
Just to play devil's advocate here, why 150s? why not step up to the 200 Verado, same weight more power (beyond 200 the weight goes up, a lot)! You're already into major $, so why not a few more $ for more power?
TJ asked if anyone had 4-stroke experience on an 18. He is looking for that kind of info. He said he does not need a lot of power, he just want twins for the fun factor. Some of us expressed our concerns about the weight. He is aware of those issues. I am interested in the results. It will be good information. jim
I have found a pic in the archives of this site with a Dyne with twin Verados. Thru some detective work I contacted the owner. The boat is a 21' showboat for the Rock Aqua Jays and has twin 250's. I talked to the rigger and he had nothing but praise for the set-up. And thanks Jim - I am looking for anyone with experience with a rig like this in an 18' version.
That Jays boat has been discussed at length here. The rigger is a member of this forum. I did not mention it because it is a 20, and the Jay's boats are all custom built and highly modified for strength and custom rigging. The Verado boat is a one of a kind with a 25 inch ransom and other modifications. They spend a ton of money on their Dynes and they are some of the best out there. Since they have such a big investment in them they tend to keep them for years. The twin Verado did not stay there long. The 750 hp and 900 hp tripples have been much more successful for them. jim