I am running Grizzled Adventurers again this weekend (third time in five weeks!) and I'm strongly considering using the Shadowdark quickstart rules on my side of the DM's screen. I like the use of a single d20 resolution system, rolling high, advantage/disadvantage, etc.
At a glance, it looks like using the Grizzled Adventurers character playbook and standard OSR monsters will work out fine, if be less deadly than RAW Shadowdark. (I run pretty dangerous dungeons in general, so it's not necessary, IMO, to make them harder.) I'm especially looking forward to no darkvision and the real time torches rule.
I will report back after the game.