Hi Tony and readers,
Since you went down the list of usual suspects;
000500.51250000 1 1 1 FB2 1 40.000 50.000
000501.13750000 1 1 2 FB2 1 40.000 50.000
all I can think of is the old PD frequency of 155.730MHz that they still hold the KEB464 license for after all these years. There's one more possibility, when they used the 453.125 repeater channel 6 was the output of the NYC sanitation department repeater, sorry, don't remember the frequency. You won't find it on the license, unlicensed low power simplex operation on the "secret channel" is perfectly legal. Bearing that in mind they could have the old Motorola HTs configured for just about anything.
Those mobiles are 30W and the repeaters are 40W, that's puzzling. You didn't mention the second repeater, did you try that channel 2? Usually the channel designations are 1, the main repeater, 2 simplex on it's output, 3 the secondary repeater and 4 it's output although it could go R R S S numbered in that order.
BTW, in the process of searching I got a surprise. One of the guys who operated a pirate radio station in town back in the late 60s now holds a GMRS license. Small world, WILD isn't it?