I don't suppose anyone has had a go at fitting Rogers bump stops to an ARP4, with coilovers instead of leaf springs, have they? When loaded my springs do bottom out, with quite a bang too. The alternative is harder rear springs, but that will harshen the ride too or get some longer springs and wind up the clearance a bit.
Unfortunately these bumps stops need a damper hoop to attach to and I’m fairly certain the 5 link cars don’t have them.