Irwin 39 keel cracking
I have a ''73, 32''. Mine is keel model, but the construction you describe, if I understand you, sounds very similar to mine. My keel is encapsulated, but was made seperately from the hull. The section was bolted on the joint faired with a lot of filler. I do not know how many keel bolts or the size.
I have had no serious problems in my 10 years of ownership with this set up. It did, at first, tend to need repairs from season to season. These repairs consisted of reoving loose filler - sometimes some small stone size chunks - and filling with West.On one occassion a large enough chuck of filler came out that I used some fiberglass tape to cover. Over the years, the repairs to the area have become less and less to the point where they are very minor at this point. At any rate, the repairs were never cosltly or terribly difficult.
I would reccommend a survey before you purchase. If those cracks and openings were not well attended to each year - I would be concerned about the keel bolts - especially if it is a salt water boat.