[old_tv_nut]

Yes, 56 uF 350v would be OK for a quick test, as the voltage there is only 25 volts, and the tolerance on multisection electrolytics is normally very wide, especially on the high side. If it works, just use it, or look for a lower-voltage rated one for final replacement. There might be some concern about a 350v rated cap not forming completely and therefore producing less capacitance, but I really don't know at what point of over-rating you would get any problems. (I never ran into such a problem in designing gear, because we never used grossly over-rated caps due to unnecessary expense.) So, I say just try it.

A 5 foot coaxial cable is not long enough to generate that much delay. RG59 coax, for example, has a propagation speed of about 2/3 of the speed of light, so 5 feet would be only 5 nanoseconds. A reflection would be delayed 10 nanoseconds, which would be invisibly close to the main signal.