driving Spartan-3 input from 74LS TTL

I've read answer record 19146 about using a series resistor for
5V tolerance on Spartan 3 inputs.

If the signal source is a 74LS TTL signal (e.g., 74LS14), what
is the maximum Voh I can expect (over temperature, etc.)? It's not
in the specs, but I know it's not 5V. Is it above 3.3V?

I'll probably just assume 5V and use a 330 ohm resistor pack, but I'd
like to know the real-world limit.

Thanks,
Eric
.