I had one of those.They area particularly nice rifle.Pretty much a small ring full length 98 action.They are nicely made.
The crack is a bummer.Obviously,don't even bother with the JB Weld.
And,I agree with dak,the default answer is a receiver with a crack in it is a "red tag" not suitable for service.No rifle is worth getting your hand or face destroyed.
If it were in complete ,military collector condition,it would have some significant value.
As it is,modified into a sporter,without the crack,in good working condition....
Because I like those rifles I might value it as high as $300(and that does not mean I can afford $300!!), I think few people would go that high.Thats without the crack.
Unfortunately,the crack is there.I would not buy it or shoot it.
Now,IF there was a compelling reason,there might be a rare individual who could assess the crack,why it happened.It could be possible ,on the rear bridge where it is,it could be TIG welded and refinished,and put back in service...with reservations.Maybe.But it would cost a fair amount of money to do that.In the end,you would still have a modified milsurp of questionable safety and not a lot of resale value.
It would be throwing good money after bad.
Better to look around in the used rifle racks and find something else.