that's quite an old boat, The Vmax looks older than a 50 hour engine and the boat claims to have new valves (it takes a long time for valves to need replacing, so I think you are looking at a boat that is oldish. Not that much of a problem with Scorps however ) I wouldn't value the engine at more than 3 k if its 5 years or so old.
that puts the rest of the boat at 15,500 without an engine. that's not a bargain. Trailer included ( min 1500 if not) are you keeping it in Spain or relocating it ( best part of another grand)
I'd take the 60 knots as being hopeful Best speed I ever got from a 6.5 with a 150on flat eater was 52 knots GPS. The extra Hull length and the Contra rotating props might get you an extra 8 knots but I'd be pleasantly surprised
Here it comes again, I don't stand a chance
Soul possession, Got me in a trance
Pullin' me back to you - Deja Voodoo