Look on line for silicon turbo boots you should be able to find the angle you need and then cut to fit and clamp, they worked great for my late model carbs.
I thank that's the best way to build, garage built and recycled parts. One off parts make it hard to replace if they fail. In my opinion that is a true custom bike that you can ride every day, not just julery for your butt.
Try a little petroleum jelly on the mating serface of carb and boot this should help seat the carbs. It does sound like the idle screws are not in sink with each other.
I would buy it sight-un-seen for $200. Get some pictures, I live in northern FL and I need a parts bikes for my current build. Drop me a line email: tqmonger@yahoo. com
850-910-3872 Brian
The cost in labor will kill any sale price or profit you want to get out of it, for something that sat for that long would need a rebuild ground up. I build custom bikes from finds like that and do it for the love of the build not for profit.