Having the 70 year model means your front passes through the k member. The biggest that you can fit without interference may be the 1.25 from Firm Feel. There are tubular bars for less weight but you also get a less effective bar. I have a 1.250 front bar on the Charger that originally came on a 1 ton 73-87 GM 2wd truck. I cut the ends off and drilled it for end links. The bar cost me less than $60 to buy and modify compared to $300 or more for a new one. The rear bar options are varied. Some feel that a bar mounted to the frame (Like Firm Feel) is better due to it being "sprung" weight similar to the front bar. It will be best to talk with a sales pro to determine the correct sizes so they will help you achieve a balance. You don't want to only install a huge front bar or a huge rear one. Its best to install moderate sized bars at both ends. Too large a front bar makes the front end want to run wide in turns (Understeer). Too large a rear bar will make the rear end of the car want to run wide, causing spinouts!(Oversteer)
I have the 1.25 front bar and a 7/8 rear bar. I am on the edge of oversteer even with wider rear tires. If I were ever to take the car on a road course, I'd switch to a smaller rear bar. Oversteer only gets worse at higher speeds. A car that has a slight understeer tendency is generally considered safer because the car & driver can often regain control simply by slowing down. A car that oversteers can be a lot of fun but you are on the ragged edge all the time.