mikey,
As I understand it, both PC-3 and PC-4's can start drawing at 60 while continuing to work, although the changes were after I retired and didn't apply to me so I'm not positive. You do apparently have the PC-3 and PC-4 benefit reversed. PC-3's get their calculated benefit, or at least most do - there may be some PC-3's that were hired older and didn't have that much service time before the pension was terminated. That's because the money that was in the plan is handed out to PC-3's first, before PC-4's get any of it. There was enough money to pay PC-3's ~98% of their full pension benefit corrected for "early retirement" penalties based on when the plan was terminated. That is greater than the PBGC guarantee for most PC-3's. Once PC-3's calculated benefit amount was set, it doesn't change regardless of when they start drawing the benefit since the amount was established based on the plan termination date which doesn't change.
The PC-4 benefit changes with the age you start drawing it since it is based on the maximum PBGC guaranteed amount which itself changes with the age benefits start.
In short, PC-3 benefits have the "early retirement" penalties of the termination calculated into the amount of the benefit, so the benefit doesn't change. PC-4's take the "early retirement" penalties based on when they start getting the benefit - start drawing earlier, get less, start drawing later, get more.
As I said, the easiest way to know what you'll if you start drawing at a given point is to call the PBGC. I've never had an unfriendly rep and they'll take all the time you need to get your questions answered. For PC-4's, the table of maximum benefits is on the PBGC website so you can use that as a starting point but you have about 6-8 options for the benefit and the table in the website only shows two of those.
Jim