My question is did the allies use the same lower hull on the Sherman all the way through its varients

The hull was most dependent on what engine was carried. The M4A4 and M4A6 had a lengthened lower hull to accomodate the Chrylser multibank engine. In photos, a prominent feature is that the spacing of the bogie wheels is greater in these longer hulled shermans. The others had basically a similar bottom hull (with requisite differnces for their differing engines, too)

Thanks