I suspect you'll get lots of varied opinions on this question. I can provide my own thoughts: the advantage of a spread bore is crisp throttle response when running on the primaries plus a bit better mileage. Sometimes it takes some tuning to get the secondary transition to come in smoothly.

I'm partial to the square bore 600 cfm Holley's myself, particularly for street driven cars with near stock engine. As you probably know they're pretty simple to work on and for myself, pretty idiot proof.

Having said that though, I would recommend you try one of the Holley spread bores. I've run them on a couple small block Chevies over the years and been very happy with the all around performance. I'm going through one right now for a 360 in a 74 Roadrunner, replacing a thermoquad that's beyond saving.

As an alternative, the Holley economaster carbs are nice running, economical carbs. I've had 2 of those over the years and just loved the crisp response. They're not as plentiful as the other spread bores in my experience, and a bit more difficult to work on.

Personally I think the 750 cfm you said you had on hand would be more than you need. Good luck!