Frank, pine does not stain well and tends to be blotchy, plus that may not cover the old paint. I'm surprised that you had paint residue after stripping, the wash, and sanding. To do anything, you will have to strip again to get the poly off. That sure should get any remaining paint also. I do use a spit coat or wash coat of shellac on many projects. You make this by adding 5 parts of denatured alcohol to one part white shellac. I don't know how much you have to do but a little goes a long way and I would probably mix up about a third of a one pound coffee cans worth to start. Apply it with a cheap foam brush. It will dry quickly and be ready for poly in about an hour. You may want to give it a LIGHT sanding after the spit coat and before the poly if the surface feels grainy, then tack cloth. Since the alcohol dries so quickly and is flammable, you don't want to apply it near sources of ignition and you do want to have good ventilation.