two things Schrom, the Edlbrock carbs are available everywhere, online, Oriely's, NAPA, and you can get one for the engine and purpose you want to run, and it will work just fine right out of the box. One of the most frequent problems people have is over carborating a motor, the 350 Chevy, stock configuration, developing 260 /300 hp only requires 570 cfm carb to run efficiently, the 600 cfm Edlebrock I'm running, actually on Barb's boat, is the #1406 carb, and there is hardly any difference in the marine application, just a little neopreme plug to close off the vacumv port for the power brake drum.
http://www.edelbrock.com/automotive_new/mc/carbs_acc/performer.shtmlSecondly, it takes a little thinking to adjust those secondaries, and that may not be your problem anyway .. you may need to check your timing with a degree wheel, or a timing tape on the harmonic balancer, with the thunderbolt ignition it needs to be running @ 32 to 34 degrees total advance @ 2000 rpm, check that fiirst, then, at an idle 600 / 800 rpm, set the idle screws forward till you hear the motor labor just a bit, thenback up the screws 1/4 turn, one at a time, that should give you a nice smooth idle. If it still "bogs" on a full throttle hole shot, then you may need to adjust the secondary thingy's. There is a slight spring with a tensioner on starbord side of the carb, and it's up side down, but if you set the tention a little tighter, so the flapper don't just fly open on a hole shot, that usualy takes out the bog ... Like I said .. it's a thinking thing ,, and that is getting more difficult for me the older I get. Good Luck ! but you may find out by messing with that you can really wake that carb up. I know a lot of folks will tell ya those carbs ain't worth a nickle, but Chevy has been running then since 1961 or so .. I really don't remember. but a Long time, and they have been using them on 4 cylinders, 6 cylingers, 8 cylinders, and I think the marine motors used them until 1996 ... so, go figure. and Yes, I prefer the old style Afb /Avs carbs to the quadrojet because I think I get a little more performance out of them, and better economy in a boat, not the same as a quadrojet, in a car, the quadrojet will get more milage, but not in a boat, it's a different bird, and I'm going to argue that point with anyone .. it don't make much sense to me, but it's a fact.