Launch velocity was estimated at 66km/s. 11 of that would be burned climbing out of Earth's gravity well leaving us with a velocity of 55 km/s relative to Earth. It will take another 42 km/s to escape the solar system, so that would be a velocity of 13 km/s at escape. Voyager 1 is traveling at 17 km/s, so would either be ahead of it or will catch it eventually.
But this doesn't account for the earth's orbit at 30 km/s. So depending on the launch orientation to orbit, the manhole cover could either still be in orbit around the sun, or have a velocity of up to 43 km/s at escape. So it's possible, if it didn't get vaporized, that is.
The Wikipedia page has the date, time, and location for the Pascal-B test:
August 27, 1957 22:35:00.0, 37.04903°N 116.0347°W
So that would have been 10:35PM local daylight savings time from southern Nevada, so 9:30PM solar time.
Turns out the potential adder from earth's rotation is a negligible ~0.37 km/s at that latitude. With earth tilted by 23.5 degrees, we have it launched 37-23.5 = 13.5 degrees away from the orbital plane. That seems smallish, so let's ignore that. Seems like the best time would have been around 6AM to add to the orbital velocity and 6PM to be about the worst, subtracting off the orbital velocity. At 9:30PM, our 55 km/s launch vector is 127.5 degrees (8.5/24*360) away from the 30 km/s orbit vector. For a combined velocity of around 43.8 km/s. Check my math.
I'm missing something from the initial calculation which is that the solar escape velocity from the current position of Voyager 1 is about 3km/s, so Voyager's velocity at escape would be 14km/s, not 17, which is very close to the 13km/s of plumbob without any earth assist. So basically anything in the direction of orbit beats voyager, and anything the other way loses.
Looking down on the north pole, the earth rotates and orbits counter clockwise. This means that anything from midnight to noon will be aligned with the orbital vector and anything noon to midnight will be offset. 930PM will be about halfway between sunset and midnight, so losing 11 km/s from orbital velocity sounds about right.
But this doesn't account for the earth's orbit at 30 km/s. So depending on the launch orientation to orbit, the manhole cover could either still be in orbit around the sun, or have a velocity of up to 43 km/s at escape. So it's possible, if it didn't get vaporized, that is.