The DC8 had no in-flight speedbrakes so reversers were used for emergency descent. The amount of reverse thrust and which reversers could be deployed varied from model to model and engine type. I was familiar with a JT3D powered version (50 series) that could attain near full reverse thrust on the inboards and idle reverse on the outboards when airborne. I only ever saw one deploy reversers prior to touchdown - a Swissair DC8-62 landing on 31 at Kai Tak was fast over the fence and the reversers were seen deploying with the main gear a few feet off the ground.
BEA Tridents seem to routinely select reverse before touchdown.