Hey XX XXXXXX thanks for the question,
Years ago my neighbor had one of these and we tinkered with it many a summer night and as I remember it had dual quads, 425 horsepower with 650 cfm, Carter carbs. In the old days the top of the carb had a little metal tag that went under one of the screws that was on the top of the carb, that tag told the parts guys what carb kit to sell for a carb overhaul. Now days finding someone with that ability to overhaul gets a little harder. Hope this helps, good luck with the 409, I think the dual quad was somewhat rare.
If this helps please accept, if not let me know, all bonuses and feedback appreciated.
Thansk,