Many members have reported success using SIS freewheels with AccuShift. However, my experience is contrary. I find that you can get good performance over about 4 cogs, then things start to unacceptable. Maybe I'm just too particular about my shifting.
Of course, you can always switch it to friction mode but you're still going to have a problem. The Sprint is a relatively narrow range derailleur, with a wrap and maximum cog size of 26T. By the looks of it, you're not going to able to lower the gearing much more, maybe 4-6T, and even then it appears that you may have to split that between the freewheel and chainrings.