Earls, Russel and some others make a line for the dp's. The one's that use just a chrome tube can give you issues when you try to tighten them up. They can leak, tube twist etc. Also lay a straight edge across the main body of the carb where the metering blocks and throttle plate go. If you have any warping, get it flattened out. You can get it milled [probably best], file it or sand it. I use a made up sanding block with some 80 grit wet or dry then 180 wet or dry to get them flattened out. Having the body warped can really give you some weird running issues. Depending on the production date of the carb, there may or may not be check valve block offs for the power valves. Holley finally did this after awhile. When you get a cough back through the valve, the power valve is generally ruptured then and must be replaced. I learned of an easy way to do a block off check ball on the throttle plate many years ago to put the kabosh on this and can hook a bro up with the info. I'll take a photo of the passage in question and give you the procedure. The little check ball[ or balls if its front and rear pv's]] are already in the Holley carb kits as just extra stuff you don't normally use. I would also suggest you stock up on bowl screw, bowl to block, block to body, throttle plate to body, idle mixture screw, pump squirter nozzle and base to manifold gaskets. You can't always get these when you really need them. Going by your list number, which I believe is 4782 for an 850 dp. you will be able to get a breakdown from Holley on all these components minus the base to manifold gasket.