Ok. I've heard that mechanical secondaries are better suited to a light car with lots of gear.
But could i really go wrong with a 750 Holley DP in the 4400( estimated) wagon?
In have this on it now.
http://www.summitracing.com/parts/SUM-M08750VS/

Would prefer something more user friendly, so i can better tune my current combo, before i go crazy changing parts.
413, 9.5 comp 906 heads, 0.486 int./0.473 exh.279 int./296 exh 107lsa, 2600 PTC converter, 3.45 gears. performer rpm intake

I'd suggest one of the vac sec holley clones w fully adjustable circuits so if later on you get serious about tuning with an LM1 you can dial in every subsystem spot on

You can make either type carb. work, that being said I would probally go with the vacume carb. and tune the secondary opening with the spring kits out there. Every driver likes different things, what I like you may hate BTW,I like mechanicals carbs as well as vacume secondary operating six paks

HEAVY car, moderate gear, automatic with a fairly tight converter. All that says Vacuum Secondaries.
BUT, I think how you drive it plays into it to. If you're a quick and often pedal-masher then VS. If you just drive the car and sometime roll into the throttle hard but not instantly, then maybe a DP would be ok.

750 vacuum secondary with a plain(no color) spring is what it will like best.
Been there and done that with my Polara many times and always ended up with the vacuum secondary for best results.
Only thing better would be a spreadbore vacuum secondary or a finely tuned thermoquad.

If you are running a dual plane intake, you'll be fine with a DP