I haven't seen this kit in quite a few years.
Yes it is an old clunker of a Tamiya copy. The hull and turret if I remember correctly were out of scale. The stowage as you have already pointed out is moulded on to the body of the kit. One plus that it has is that it is an easy-8 suspension and I believe this is workable enough to use on a different kit all together to make a later version Sherman.
As far as using an AM hull ... I'm afraid that dimensionally it wouldn't work (I could be wrong on this though)
There are to the best of my knowledge no AM upgrades available for this kit.
And sanding down all the details and using PE would be excessive in the build of this kit IMHO.
You're other option is to build it the way it is. It's definitely not up to the standards of the kits that are produced today, but what the heck, it's still buildable.
Hope this helps a bit !
Happy Modelling and God Bless
Robert