I was told that I could sign up for social security before I reached 70 years old, collect that amount and then sign up for my eligible Railroad Retirement at age 70. The idea was that I could collect the maximum amount from them because they make up the difference in the total amount as if I'm 70 years old and I won't take the lesser amount that the Tier 1 would be had I signed up earlier. As such, I would be able to collect SS early and also get the maximum amount later from Railroad retirement. Is that correct?
As far as I know that's possible, but I'm not an expert on Railroad Retirement (RR) benefits so you should probably check with the Railroad Retirement Board (RRB) regarding your RR options. I can confirm that if you've paid into Social Security long enough to be eligible for Social Security retirement benefits you can claim those benefits without being required to also file for RR benefits. However, if and when you later apply for RR benefits, the RRB will offset your Tier 1 RR benefit rate dollar for dollar by the amount of your Social Security benefit rate.
You could potentially file for Social Security retirement benefits as early as age 62, but if you claim benefits prior to your full retirement age (FRA) your benefits could be subject to full or partial withholding if you're still working and you earn too much (https://www.ssa.gov/planners/retire/whileworking.html). You could, however, draw your Social Security benefits starting at FRA regardless of how much you're earning.
Another possible option would be to first file for RR benefits, then file for your Social Security retirement benefits at age 70. You can accrue delayed retirement credits (DRC) on your Social Security retirement benefit rate from FRA to age 70 even if you're drawing RR benefits during that time. I don't have enough information about your available options, though, to be able to give you any advice.