@Babin Farms Thanks for the tag-in.
@jet boat joe Short answer is that there isn't a "stage" style recipe for going faster in the 19ft boats (or any of the Yamaha boats for that matter). Everything is much closer to a "one off" modification than anything. Lots and lots of "guess and check" sort of work.
Have a look at these threads for inspiration.
https://jetboaters.net/threads/adjustable-trim-and-directional-reverse-bucket-install.17569/ <--If I remember right, the trim helped pick up speed for Sam.
https://jetboaters.net/threads/maptuner-x-192.17574/ <--Some discussion on MapTunerX
Not sure you're going to get an AR195 into the 60's without significant work. Appears the hull is stable at that speed, just a matter of both generating the power, as well as getting it transmitted to the water. Lots and Lots of work, with marginal gains at every step. Definitely have to get a tune to raise the rev limiter, anybody with any serious speed has that. Boosted guys are all running aftermarket intercoolers, tunes, modified impellers, and lots of little tweaks along the way. In particular, that second thread has most of the 19ft speed players in it. It's a rabbit hole of reading, but going through the post history of those fast guys will get you a LOT of the details you're looking for.
Keep in mind that bow loading is absurdly influential in the speed a 19ft hull makes. Adding weight to the bow does two things; 1. It adversely affects the direction of the thrust on the hull. Put the bow down and the thrust points slightly more "up" than "back". Driving the bow further into the water. 2. Increases wetted surface. More boat in the water, generally, means a better ride, but more drag. I've seen as much as 4mph drop by moving 300lbs of people from the stern to the bow, with otherwise similar loading. I also have the best holeshot and tubing experience with most of the "people weight" in the stern seats, everything else being equal. You're likely to find a few mph by just ensuring you're well balanced fore/aft.
If you really want speed from a Yamaha jet boat, your best bet (IMO) is to find an older 210SS. These had the twin 1.8L engines with a short windshield and no tower in a small 21ft hull, or look into a 212S from the '12-'18 era, also twin 1.8L in a 22ft hull. Those are the two "easiest" setups to go fast while maintaining the gold seal durability Yamaha is known for. As best I can recall, the SS was tickling the 60mph mark bone stock, and the 212S will readily get you into the mid 50's bone stock. Lots of value in that kind of speed with zero modifications.
Coming from a life of modifying and generally monkeying around with all things mechanical. The further you move away from stock, the more likely you are to have unplanned downtime. Keep that in mind if your boat is used for family time. It's one thing to suffer a failure while out with your buddies, it's something entirely different to endure that with a wife/kids/in-laws aboard. Being on a boat makes that amplified as help is often much more than just a crappy hike home away. Just a bit of unsolicited advice from an aging gearhead. With that said, sounds like fun if you have the time and budget to make it happen.
SamCF ran into this problem here.
Finally......I've always thought it would be neat to find a 212S, and modify it with twin SVHO supercharged engines and the appropriate supporting mods. I suspect we would find that easily into the 65mph range, if not more. No idea if the hull would hold up under that kind of speed, but I'm just waiting for someone that's bored with a big budget to get that done!
