As they say in show business: It'll be a tough act to follow. Following the record-breaking opening weekend of "Jurassic Park," the film industry is poised for Friday's opening of what has been expected to be another potent box-office force, "Last Action Hero" starring Arnold Schwarzenegger. Whether that conflict develops or whether the marketplace simply expands remains to be seen, for even in the unlikely event that the audience for "Jurassic Park" is sliced in half, it's still on a runaway-hit track. On Monday Universal released a final weekend tally of $50.1 million, which confirmed that the Steven Spielberg horror film had set a new industry record--surpassing the previous record gross of $47.7 million for 1992's "Batman Returns." The $50.1 million includes $3.1 million that "Jurassic" took in from Thursday previews. (The "Batman Returns" opening gross included $2 million from a similar preview.) "Jurassic" is playing at 2,404 theater locations, showing on an estimated 3,400 screens. "Action Hero" will open at 2,300 theaters on an estimated 3,100 screens.