I just went back and read your initial post. Here i'll help you with a reply:
chances are the short block will have better pistons, and better camshaft with a double roller timing chain (if it comes with the cam and timing chain) and if it does come with the camshaft all you'd have to do is convert it from the 302 standard firing order to the HO/351 firing order. Chances are that the HO will be a non-roller cam block.
If i were you, i'd just go for the HO short block, you shouldn't have any problems with it.
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previous name: 84stangLX
'84 Mustang 5.0 LX
my LX
'89 Mustang GT
my GT