Fresh rebuild years ago, has been sitting with no fluid, just started new rebuilt 460,runs great. put in 6 qts type F, cranked engine without starting(forgot to fill torque converter) started engine, put in 6 more qts, little or no fluid circulation through transmission cooling lines. I have a piece of clear tubing connecting the pressure and return lines together. I have not driven it on the road, just pulling it in and out of garage. Should I be seeing fluid flow?

 

12 quarts sounds low to me, check that. If the clear tubing is filled with fluid, no bubbles, can you really SEE flow?

One unrelated observation... for years now, C6's that were pre-changeover date (those built for Type F, among other things) have been rebuilt using Dexron III/Mercon compatible clutch frictions and band. Not sure if Type-F frictions are available anywhere anymore. Do you know what ATF your rebuilt trans was supposed to use now?

IIRC, using Type F in a Dexron III/Mercon frictions trans yields a "grippier" shifting characteristic, and some hot-rodders do it that way on purpose.
I think going the other way, using Dexron III/Mercon in a Type F frictions trans leads to failure.

 

Think old Chilton's manual I have says 24-26 pts, shows where it should be on stick. Clear tube has some fluid on both ends with air in between, have not seen circulation when running. Now that I think about it the guy that rebuilt trans may have said Dexron/Mercon.

 

What does level on dip stick show?
Does vehicle move?
I would not worry about cooling line flow till you have correct level on dip stick and vehicle moves forward and backward then recheck dip stick.
Why are you checking cooling line flow anyway.
Installed 100's of trans but never checked the cooling line flow.
That said the return cooling line goes to lubricate the planetary gears so you do need it.

BTW:
Worked at many trans shops over the years back when. The last Aamco was the best of the bunch. It is the same problem with any franchise. Any schmuck with the money can get a business. All the company support is for sales not technical know how or honesty.