Gravity hot water system trouble

I live in a 3 story twin. Gravity hot water system, not sure if it's open or closed. I have a large overhead tank in the basement above the boiler and there appears to be an overflow pipe coming out of the roof right at the highest point in the system. The boiler is a Weil McLain type D. If I had to guess, anywhere from 40-70 years old. Jacket is a metallic blue.



The problem is the top two radiators, the ones that flank what I believe to be the overflow, do not get hot. I've bled air from the whole system bottom to top, and I'll get water out of those two, but they never get hot. Even cranked the pressure up quite a bit, and nothing. Thing is, I don't want to spend a dime on this system. Makes more sense in my mind to put money toward a new boiler with forced hot water. I've already cobbled together the rotted burner drawer pan with some angle iron and screws just to kick the can down the road for another winter, but I'm not willing to get a pro out on this because that would mean at least a few hundred bucks. I just want to see if I can get those last two rads hot since we've been using those rooms now. I appreciate any helpful advice. I can provide a diagram of the system if necessary.