Reason I am using 186 foot doublet, I believe 186 foot is it is a 3/8 wl of top band. Also, I am told, it should be a great antenna on 40m as 172 foot doublet acts as an extended zepp (1.25W on 40m).
Umm, I have no idea where you got these ideas. 3/8L has no practical bearing on cutting dipoles lenghts. Second, a dipole isn't a Zepp, so 1.25L again has no significance to your installation.
Your dipole is resonant at 2.51Mhz. (468/186ft = 2.51Mhz) [thanks for giving us backwards colonials dimension in ft]
You aren't able to get in a full dimension for 160M. Trying to use a dipole below its resonant frequency can really cause problems due to high voltages in your tuner, etc. For better performance I would suggest shortening the antenna to 80M length. That should then tune very well on 80, 40 and 20, the other bands will still depend on the tuner to match.
If you want to work 160M then attach a shorting jumper at the bottom of the ladderline and work the antenna as a T against ground. From another perspective that is an Inverted L with two horizontal portions. (You can add radials to help).
That is what I would recommend. Good luck! Bill
p.s. I would argue that any lower noise levels on the Cobras is due to higher losses.
p.p.s. If you are determined to work with this antenna, try changing your feedline length.