So my neighbor is thinking about a great deal on an old Mazda which the owner "thinks has a blown head gasket"

I told him it's chancy because while a head gasket proble may be fixable without tremendous  expenditures (though getting a rebuilt head seems almost a 'given' need), if the block is cracked or has an uneven surface, that's going to be major money, and I don't know of a way to tell if it's one (head) or the other (block).

Is there a way to tell the difference?

I told him to look for bubbles / oil in the coolant or coolant in the oil, but that's about it.  Oh, yeah also that a compression check would point to one or two cylinders, but that's about all I could say.

Any tips?  I really think  he should avoid these vehicles with internal engine problems.

Unless the guy is a real competent do it yourselfer, why buy trouble.

IIRC the Mazda piston engines use a cast iron block with aluminum head. The probability of block damage is low unless it suffered a MAJOR overheat and the driver kept going until it stopped.

i had repaired a blown head gasket on a isuzu i-mark twice. both times it was leaking coolant externally, never got into the oil.

i'd find out what makes him think it is a blown head gasket (ie coolant in oil or external leak). cost me less than $250 each time.