AW4EVER;
I'm sure its possible to complete an 80% lower without a copy of the blueprint, but it sure is nice to have one to refer to. Measuring off of a manufactured lower is fine but it gives you no concept of the allowable tolerances.
There are PDF files of D.Sniders lower receiver print (the one that almost everyone works off of) scattered around all over the web. The link below is to the file posted on this board. The same file is also posted over on Roderus Custom Gunworks, biggerhammer, and probably dozens of other places.
old.ar15.com/docs/lowerBlueprint.pdfJust pull it up and print it out. It's a bit hard to read on an 8-1/2x11 printout but if you've got access to an 11x17 (or larger) printer, it's no problem.
If you can't get it to print for some reason, e-mail me and I'll send you one.
HTH . . . . Doug