+1 on getting it welded. I would say try the JB weld since there's not much to lose, but since you already have an existing vacuum leak you could drive yourself batty by introducing another one. I'd also check and make sure the manifold it bolted to is machined flat - normally the bolt would strip before anything cracks. Who knows, it could be the source of the original vacuum leak.

Sorry on the bum luck dude.

 

im not too worried about it, this isnt my main carb, i have a nikki on it now, and am waiting on my sterling. this is just a project. ive already chaulked it up as a loss. and as far as i know there may have never been a vacuum leak in the first place. ive been through like three side drafts carbs and have had any of them to run properly. once i can get the throttle shaft out. im going to grind down the crack and fill it with jb, then rebuild it.if it works maybe i can get a slight return on my investment.