>>Is there a big difference...<<
Nah. This is a heavily hyped area of hot rod parts sales, but there's no free lunch in electricity, either. Manufacturers can vary the ratio of primary windings to secondary windings, this manipulates the maximum output voltage, but the tradeoff is that the amperage is reduced by a corresponding amount. If some coil is advertised as producing a gazillion volts, then there's probably no amps at all. I've now gotten to where I don't think there's much of anything to be gained until you move up to a system that doesn't use a resistor on the input side of the coil, like a GM HEI, for instance.
If you do want to have a fancy coil, look up what Mallory recommends for the distributor you've got. Probably one of those big square black ones. They're pretty reliable, unlike the big yellow ones. There's some small round red ones that seem to work OK too.
Does your Unilite have a vacuum advance?
Tom (if you have a small round black one that says "Delco-Remy" on it, I'd consider keeping it if it was me. They make good sparks, last forever.)
[This message has been edited by tommob (edited 05-19-99).]