Thanks to all for your help on this ferrite core question.

The objective was to see if I could put up the antenna with only what I
have on hand... and I have a 50-foot length of RG-8X and four of those
radio shack ferrite cores. I also have an MFJ unun and so I could cut the
coax at 22 feet and put in a couple of coax connectors, and use the unun,
I just hadn't gotten around to doing that and anyway I don't have the
connectors (but, the Radio Shack is just down the street).

Someone said "try it and see what works", so I did that... put up the
antenna this afternoon. Unfortunately it started raining and the XYL
started yelling at me to get my @$$ off of the roof before I fell off :-),
so I didn't get the unun OR the ferrite cores installed yet.

I figured what the heck, may as well try it without the choke and see what
happens. I inserted the unun into the line where the coax comes in the
window and fired it up. It actually seems to work better than my inverted
V on 20 meters (only band I've tried it on so far), though the difference
isn't exactly what one might call dramatic. Also the SWR is pretty poor
but nothing the rig's internal tuner can't handle.

I'll get the cores or the unun up there tomorrow and see how it acts then.