Not to lessen the previous advice, as long as they look externally the same, they will work.
Had this problem a couple weeks back. Looked at 4 starters at LEAST, that were all stated as being for various 73-87 truck applications, not a single one of them was identical. Bigger or smaller solenoids, different length starter bolts (not cheap new, $6/each) cast iron or aluminum noses, bolt to bellhousing or block, staggered or straight bolt pattern, and so on.