Let's see... when did they start using pop-offs on GMC blowers, was it 1955...?
A simple cover plate, loaded in place with a calculated valve spring and installed with gasket sealer (after all, it's a safety device not a regulator) will cost, what - $10.00?
Since this is EFI, only hot air is vented and shouldn't disturb anything, so no duct is needed.
Safe vent = 4 × 1.5" holes (7.1 sq." area) with a hole saw, with a 6" × 6" × 1/4" thick rectangular plate across the top.
A 3/8" hole (valve stem size) centered between vents, 3/8" bolt inserted through the roof (or your choice) of the plenum from below with thick big diameter washer under the head (pin the bolt in place, or make sure you can reach it from inside). Bolt goes up through cover plate by 2", secured by lock-nut and valve spring collar. 7.1" area × your boost + 5 psi. E.g., 20 psi expected, 25 psi × 7.1" area: the plate will pick up against 176 lbs. of spring tension, but just barely.
Remember, just cracked may not vent excess boost as fast as the compressor is supplying it, so don't assume a pressure drop is a done deal.
1 big triple valve spring should do it, test with a compressor for cracking pressure. It may need to lift 1/2" to vent everything, so a big spring is needed.
More vent area? Bigger holes, more holes, 2 springs etc.
Carbureted? Must exhaust only into a safe duct, and pass outside the vehicle without going near exhaust, electric, rider, etc.