351w is a common swap, but you won't be able to keep the stock hood, you'll have to get a cowl hood to clear the intake. Maybe a carb engine would just make it, I'm not sure.
As for largest engine, I've seen 460's in mustangs. Not a simple swap but it can be done.
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'92 GT conv.
TFS heads, GT40, Powerdyne 9#, AOD, 3.73...
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