Hi Portage Bay,
Well, it appears you've already had your mechanical survey, so input at this point is sorta moot. But, it's been my experience, having witnessed (and paid for!) mechanical surveys on multiple boats, that it's very difficult to issue a broad-brush opinion on "...what to expect with a pre-purchase engine survey." Even narrowing the field by including only older, mechanically-injected engines still leaves you with a giant list of "older" engines, each with a different set of procedures necessary to assess their health.
Unfortunately, it's on you to determine if your surveyor of choice has sufficient expertise to provide you with the information you require to determine the health of the mechanical items aboard a specific boat in question. But if your mechanical surveyor returned a survey "...more like a report for insurance." you may want to re-think what you really need to know from such a survey.
Typical engine surveys (and generators and transmissions, if applicable) generally contain much deeper levels of information than the number of hose clamps visible on a hose, and fuel hose markings. As applicable, oil sample interpretations, performance parameters during sea trial, crankcase pressure, compression test results, air box and ring inspections, vibration under load, etc.
I would heartily recommend that your engine surveyor be aboard for sea trial. Much of the vital survey information regarding engine health can only be obtained while underway. Lots of boats are purchased remotely, but the buyer must insist on competent survey personnel be present throughout the evaluation period. Otherwise, you're treading on thin ice, and can end up with a can of worms.
Hope this helps.
Pete