Nick, I think we paddled last summer or maybe two summers ago on the Joe Wright Spencer Heights. NF Popo has been done a couple times and you want to hike in from the Dickinson Park side. Looks like you've got it right on the map. It took both parties two days from the hike-in point. On the first descent they tried for a one day and got overnighted and wished they had their fishing poles and bivys. Second party planned for an overnighter and reported a great but demanding run.
Way too much snow still up there now, especially this year. Probably be mid July this year before you can get up the road to the hike-in but it might be earlier. The Popo melts earlier than the Little Wind drainage but I think there is a pretty heavy snowpack up there. Maybe somebody in Lander can chime in on the snowpack situation. The Sinks Run on the Popo is probably high and fun right now but that's mostly what you've got right now.
Cub boater: "What do the spiders mean?" Old fart boater: "Trust your intuition." CRCII