I'm not from the area but have a couple of comments/ideas.
Don't just look at a shop, but the person actually building the engine. You could have three guys in a place, with only one or two that really know what they're doing. Talk to them enough and make sure the guy you've talked to actually does the work. Warranty's are a separate issue, but you're right, how they respond when something goes wrong is a major factor for me and it says a lot about the company.
The other thing is if you can't find anyone nearby I guess I would consider a crate motor. I don't know what you're rebuilding, but GM has a pretty good selection with warranties and I've read that this is a good option sometimes. IIRC, some of the magazines have recommended this while swapping out a cam or other minor things.
I don't know anyone but if I was new to Florida and needed engine work I'd call a person I know I'd trust and that would be Frank @ http://www.prodigycustoms.com/contact/
He will not steer you wrong.
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Dave
FUeL 69 Camaro RS
68 Corvair coupe
65 Impala SS
65 Corvair convert
64 Corvair Rampside
62 Corvair Greenbrier