The kits offer a bridging plate for the solenoid terminals rather than having to make your own. Plus they toss in a few fusible links for safety's sake. The solenoid itself is nothing special.

I drove my 'bird to visit Gary Plowman across Michigan, and had to stop to fill it up shortly after leaving his house. The engine was still very warm after the long freeway ride and following heat soak, and although it started fine at his house by the time we'd put on a few dozen miles it was good and warm again. I had to back the distributor off about 3 degrees so that the starter would turn over. That's a classic hot issue, and I have stock manifolds. The demand for current is higher than what my 3 year old battery will deliver through older cables to the original starter. When cold and with normal around town driving, all is well.

One of my winter projects will be to replace the battery cables. That 60" positive cable is probably housing internal corrosion.