Going to look at a 1981 Viking 46’ Sportfish with DD8V-71TI

I'm going to guess they'll give you about an 18kt cruise, normal for the time. Today's boats average mid-20's. But you're used to those speeds with your Tiara. So if that's ok with you I like the old motors.
The list of what to look for is too long to list. That's why surveyors are recommended, but bringing a moisture meter to check the hull and decks wouldn't be a bad idea. Pay special attention around stanchions and through hulls.

Not in a million years.
18-20 knts max cruise.

You're going to have to go deeper into your wallet. I can't think of any production SF from that era that'll cruise at 24kts. Maybe something like a Rybovich or something custom.

Now there's some good advice. It's great to be retired. Only thing to fear in a pee test these day is a report of high cholesterol. Still not while driving though.

I am pretty sure I purchased the boat you speak of. When I left Port Washington she cruised at 15 knots at 1700 rpms and hit 20 knots at 2000 rpms which was full throttle. I think she would cruise a little faster if trim tabs were working. I love the boat

You are WAY over-propped. You need to see 350 more rpms at WOT. Is the bottom clean? If yes, it sounds like you either have a serious HP issue, OR are seriously over-propped, which will lead to a much shorter engine life. BUT, you also need to get the trim tabs working and do another seatrial.

I think the props on the boat now are 3 blade 26 x 26 not sure if they are the correct ones. I could have a hp issue due to the fact that the injectors need to be replaced because at least four on the port engine are sticky. Did not have chance to check starboard engine. My plan is to replace all injectors. The trim tab issue is broken fitting on cylinder ,they are instatrim boat level brand not sure how to remove pins that hold piston to tab. boat is in water now. The boat seemed to ride very bow high. Any experience changing trim cylinders while boat is in water while not being a diver . when I purchased the boat it had not run in years. I got the boat running and made the 36 nm trip with no issue. Now I will start to correct everything "project Boat"

Fix injectors first. Boat levelers can usually be changed in the water by a diver since they have external hoses.

I have 8 injectors now my suppler only has 6 left waiting for two . I was hoping to change trim piston by reaching in water from dingy will check how far a reach it is today .I don't want to pay for a diver. Not sure how the pins are held in place on the trim pistons

I forget, I had boat levelers many years ago. But was easy to change in the water on my boat at the time....., connect the hose first before trying to connect the ram to the tab......

I need to figure out what holds the pin in that holds the cylinder to the tab and bracket

I have all tools required for Detroit, been a heavy equipment mechanic for 30 + years did use engine serial# to verify n90 injector

I believe you have the Nylon ones and they're just driven in, give them a call and verify, but like this

CYLINDER PINS - Insta-Trim Boat Levelers (insta-trim.com)

Looks like your engine has the small injectors......or they were derated at some point in time.....most of the 8v71 TI's I've seen have the N110 injectors.......