Hello Jeannie. First of all, most of your questions require more information. I am not sure what CT 1-3 means, but I assume that 750 CA means 750 Cranking Amps. That is a high spec as 475 CCA battery is acceptable. that is 475 Cold Cranking Amps. The original size battery is a 2N which is the BCI group number. BCI stands for Battery Council International and is a trade group for battery manufactures. Group 1 is the size used my most 6 volt cars dating back to the 1920's Ford used a smaller battery case on cars in the 1950's and that is group size 2N. There is also a group 2 and a group 2E. The 2N battery is 10" L, 5 9/16" W and 8 15/16". this battery will fit the original tray and will also be the correct size so the original hold down will work. The size 1 battery is 9 1/8" L, 7 1/8" W and 9 3/8" T. This means that the battery is taller than the 2N and may cause the terminals to short out when the hood is closed. You may want to modify the battery tray to accommodate the wider, taller battery.
The clicking you get means one of two things. Either the battery is weak or you have a bad starter relay. It is unlikely that the starter relay is bad, but it is possible. The most likely cause is a battery that is bad or undercharged.
Battery cable size is important. That means ALL the cables, the one from the battery to ground, the cable to the starter relay and the battery cable to the starter must be larger than a corresponding 12 volt car. 12 volt cables are often in the 4 gauge range and will work under IDEAL conditions, but you should use O gauge at minimum for the cables. OO is even better. If you don't plan on showing the car, you can find the size 1 battery for less money than the 2N and it will also be easier to find when you need a replacement.
Remember that Ford 6 volt systems are Positive ground. Do not install a battery connecting the ground cable to the negative side. It will cause problems with your radio and dash gauges if you do so.
