The Mariner 5 spacecraft was the fifth in a series of spacecraft used for planetary exploration in the flyby mode. Mariner 5 was a refurbished backup spacecraft for the Mariner 4 mission and was converted from a Mars mission to a Venus mission. The spacecraft was fully attitude stabilized, using the sun and Canopus as references.
I’m wondering if NASA retained the 4 solar panels for the Mariner 5 mission to Venus, as other Spacecraft to Venus (Mariner 2 - 1962 and Mariner 10 - 1973) only used two solar panels as the mission took place close to the Sun

IIRC, the existing solar panels were flipped over to face the opposite direction. Do not recall anything about any being removed.

Mariner 5 did not fly the partially succesful solar lightpressure stabilizing vanes they had on the ends of the solar panels on Mariner 4. These were more or less an engineering experiment to use automatically angle-adjusted <don't remember how, it's in the JPL TR series final project report volumes> light-reflecting vanes to fine-tune attitude control. They didn't adjust properly, were mechanically sticky or something, but did no real harm.

They also removed the scan platform which was only used for the TV camera and the wide and narrow angle planet detectors, and repositioned some and replaced some science instruments, for example adding the Stanford dual channel occultation receiver.

Mariner 4 did not fly the mission designed ultraviolet photometer which was intended to look for atomic hydrogen and oxygen in the upper atmosphere. It had electric arcing problems or something that were not resolved by the time needed for flight acceptance, and a mass and electrical dummy instrument was flown. The fixed instrument flew to Venus

There isn't a separate 1962 Mariner II to Venus topic and as I didn't want to start one, I'll add a nice image in this Mariner Venus topic:

1962 flyby as seen from Earth:

To retain the existing attitude jet design, which were on the ends of the solar arrays, the Mariner 3/4 panel structure was kept, but the solar cells were shorter, as shown in these two pictures of Mariner 5 (Mariner E). They were put on the sunward side, which was the anti-sun side on Mariner 4. The antennas were put on the bottom of the original spacecraft bus, with a thermal shield on top.

Rob