Howya Martin, welcome to RIBnet!
Nice SIB, I used to dive out of those. With the console, controls and trailer, it's very attractive. Check that the inflatable keel tube is sound - I can't see it in the pic, which is a worry... The steering is going to be cable so can't be the biggest worry in the world. Probably needs new cables or a good service. I'd be checking the deck sections for damage too, especially where they fit to the rails along the tubes.
The engine on the other hand probably belonged to Noah and is worth squat. If it runs, it runs - bonus. I'd say do a compression test (not rocket science) and see it running.
If I were you, I'd price up the SIB and trailer (with console) as new and base the purchase decision on that. I really think the engine is a red herring, it's good if it goes, disregard it if it doesn't (unless you're a mech, but I'm thinking you're not