replace steering box on 2001 GMC Savana 3500

I am replacing my steering box, but I cannot separate the steering column shaft from the input shaft on the box... I loosened the retaining bolt, but cannot get the collar to spread apart from the splined input shaft. I tried blunt force with a hammer and then heating with a plumbers torch (map gas), but to no avail... any secrets, hints, or specials tools? GREATLY appreciated!!!