Here is a URL for design/implementation of "non-standard"
baluns/transformers, but of a highly useable and desirable nature--or,
Dr. Sevick strikes again!:

http://www.highfrequencyelectronics....104_Sevick.pdf

Fig. 6(A) is very interesting. A 5-winding, 1:1.56 bootstrap
transformer which provides 50/75 ohm connections/substitutions. Perfect
for allowing one to use 75 ohm "junk" (or found in dumpsters) tv coax in
place of more expensive 50 ohm coax.

I have made good use of this since I have thousands of feet of NEW 75
ohm coax I purchased from a scrap dealer for next-to-nothing! A lot of
large dia coax and hard-line mixed in!

Regards,
JS
A little mismatch isn't such a problem. At least if you can get the loss
down. I wouldn't even worry about it, the internal tuner would make short
work of that. Look out for water damage on that stuff though. Especially
the Aluminum braid/foil shield stuff like LMR. Even a little bit of
moisture percolates all through the braid.and turns it into aluminum oxide
powder and extremely noisy with power on it. It could look brand new and
you would keep cutting it back, then find a foot of new braid but keep
cutting and its back to chalk. We would routinely assume it bad and throw
it away. At least with the Hardline, you can sweep it and put some power to
it to check the loss Only hardline allowed on towers.