Jon,
I would guess the J spring will hold the forend on as well as the spring/roller used later. First I would check to insure the forend loop is secure and not loose on the barrels. A beavertail puts a lot more stress on the loop than a splinter does, that is why on the graded guns Fox used the re-inforced loop design. With theh J spring out, make sure the forend iron bears snugly against the rear of the loop; if it does not I would correct that, I suspect that is the problem. A new J spring may be needed. But too much pressure of a J spring can lead to a loose forend loop so watch it. If that doesn't work try altering your loop to a roller style.
