Do you NEED to seel it in order to fund the 77/357? If not, hold onto it. If so, then consider selling it.
Just realize that you hear repeatedly on this board folks lamenting getting rid of guns. Rarely do you hear them say "I wish I WOULD have gotten rid of XXXX"...
A .223 bolt has some good uses: varmints, target shooting, deer in some states. And t's got more range than your 77/357 will have.
NRA Life Member