You won't be able to justify Webers from a cost or performance standpoint, as there are far cheaper and easier ways to make more power. BUT...if you have the same desire for Webers I had, there's just no substitute. The look, the sound, the throttle response, that on/off feel of power, the history behind them, and the WOW factor are just too much to pass up!
I have 48 IDAs with the original-style waterneck manifold on my 363 stroker, and after a lot of reading and attempt to quickly educate myself on Weber tuning, I was just too eager to drive my car and decided to hand it over to someone more experienced and have it tuned on a chassis dyno. I just got too anxious after a couple months of tinkering and trying to figure out why cylinders would quit firing and I couldn't get rid of that low-rpm flat spot. I just wasn't experienced enough to interpret plugs, side-pipe deposits, smells, sounds, feels, etc. While I'd love to learn the art of Weber tuning first-hand, it was nice getting my car back with the things just screaming at WOT, and I don't regret it one bit. Just keep in mind this'll cost you...but as I already hinted at, Webers aren't cheap and easy.
But whether tuning them yourself or having someone else do it, I offer an additional piece of advice, and that's to keep in mind a chassis dyno will be your best friend; I was surprised after I heard how much the jetting changed, even thought the Weber builder was given all my engine specs, including my custom Weber-specific cam.
Also keep in mind that new Webers aren't necessarily perfect Webers. You'd think float levels would be consistent, passages totally clean and free of debris, etc...but that's not always the case. I was very surprised to learn that such precise pieces of machinery can be so far off, right out-of-the-box. And even though some of the distributors claim they're ready to bolt-on, that 999/1000 chance of landing the correct combo off the bat is probably accurate. Just because you provide your engine specs, once you get on a chassis dyno, you may be surprised how far off the jetting ends up being.
I've only had my dyno-tuned Weber'd engine going for a couple months before cold weather hit, but so far I wouldn't trade them for anything. I don't have experience with IDFs, either...but they just don't offer the original look of the IDAs. I imagine many are deterred from IDAs due to the lack of any choke, and the fact they've always been sold and marketed as "race" carburetors. However, I've never had any trouble starting my car, whether hot or hold, in 80-degree humid weather or in 50-degree dry weather, so I don't see any need for a choke. I do hear popping quite often at idle and deceleration, but that's probably due to my mufflerless 3" exhaust with x-pipe. Depending on how healthy your engine is [as I've heard higher output engines are easier to tune with Webers], 48 IDAs can be perfectly streetable.
And FYI, in case you're wondering about filters, I've heard good things about ITG, and have called them about setting me up with something for IDAs with the '65 GT350 hood. I don't have anything yet, but plan to have something by spring. I still have to get them clearance dimensions before figuring out what will work. Supposedly these filters are the least restrictive of anything offered. It's just insane how much power many of the available filters can rob a Weber induction.
Below are a couple pics of my 363 that made 375rwhp and 408rwtq at ~6K rpm using AFR 205 heads, Inglese Stage 2 Weber cam (mild, Weber-friendly 115 LSA, 5.0 firing order), 1-3/4" FPA headers and 3" side-exit exhaust with x-pipe.
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