I have never paid any where near that for any intake/carb combo. The most expensive piece i bought was a mopar 6 pack intake with carbs for something like 300$. Of course this was back in the day before the internet and it was used. Look on ebay-craigs list for intakes/carbs. I buy used stuff, and with some cleaning up and carb rebuild it will work like new. I like holley carbs because they are easy to work on and you can get anything you for them. Intakes the worst thing you will come across is the bolt holes for the carb are stripped or broken off. A weld and a heli coil and it's fixed. If you have a bone yard near you you can get everything you need for the ignition as long as they have vehicles from that era witch today seems to be a problem. I'm sure you can get it off of ebay with some looking. If you have swap meet near you they are a great source for parts but the season is over until spring. And for the vac advance on the distributor you need throttle vac not manifold vac. Using manifold vac will give you full advance at idle and drop off (retard the ignition) during acceleration(opposite of what you need).

 

By chance did you ever get this problem solved. I have a 87 D150 doing the exact problems. Only thing i haven't replaced is the distributor and the lean burn box.

 

Rather than continue an old thread, where you will get lost in the shuffle, post a new thread. Detail all the items regarding it. The year, engine, what you've done, what the problem is and so on. Especially the miles on the engine. Then we can all pile up on you. Seriously, there are enough retired and currently working mechanics and tinkerers that we ought to figure it out.

 

I am restoring a 86 w150 short wide 4 speed granny. And when this truck was doing that I replaced a part on the carb on the right side here is a pic of it . And the cost it stopped all the issues even the dumping gas into the oil. I am putting on a hei distributor 4 b carb and manifold . But this was to get it going while I purchase parts as they are hard to come by and not all of them cheap. Best of luck to you

 

That IS a Lean burn. They moved them off the air cleaner to cut down on heat and vibration, a common reason they went bad.
I had 2 Diplomats over the years. 1 was police interceptor version. That one had the LB behind the battery in the fender as well.
OP is on the right track to $#!tcan that lousy ignition system. You will need a different distributor AND carburetor. You need a carb with a vacuum nipple for vacuum advance, and of course a distributor with vacuum and centrifugal advance