For a quick (and most importantly) light weight spool or locked Diff, don't use putty or jb weld. Too heavy, too much rotating mass and won't dry evenly (wobbles). Use gorilla glue or expanding foam. The gorilla glue bubbles as it drys leaving a hard foamy mass, and well the expanding foam.... Expands.... Both will give you a lightweight locked Diff.
A very important upgrade a lot of people over look when locking their Diff is the slipper clutch (the last line of defense your axles have) . A good consistent and reliable slipper will add a bit of survivability to your drive train.
"The predator lives alone, he accepts this reality as the cost for his existence "