depending on the type of freewheel and how threaded it is as opposed to splined, you could spin off the outer cogs, slide off the splined cogs, spin 1 of the threaded cogs back on and hope you got a perfect chainline with one of the chainrings. I did this when I first converted my bike and lucked out. Otherwise, cop a bmx freewheel and have someone redish/respace unless you can do it yo self. Good luck.