A 60' flat top for 160 and 75m!

[WA1GFZ]

Yes Frank Step down would be fine but only if it is at the feed line. Maybe you could consider a remote controlled tuner. 
Warren K2ORS has been playing with step down for his 137 KHz loop antenna.
Again the tuner is at the antenna.

[WU2D]

Here you go Frank - A 6' flat top.  You will need a tuner.

Mike WU2D

[The Slab Bacon]

Frank,
         I took a few initial measurements last night. Found that 2 conductors of #8 THHN wire laid side by side measure right around 7/16" which is just an RCH wider than RG-8 coax. With that said, a bifilar wound common mode choke balun made of #8 THHN Should be no larger than the one using coax, and the same numba of turns should take up pretty much the same space. Also looked at the connectors for LDF-450 hardline (1/2" hardline) and found thet the center conductor is just a grunt bigger than #8 wire. It should easily take the pounding.

                                                          The Slab Bacon

[WA1GFZ]

That should cut the resistance in half. Good Luck!