Can only answer some of your questions....

I put a new style barrel on the old style so had to buy a new bolt because you can not just swap out bolt heads. It fit fine but you do have to grind the little groove off of the bolt baffle- because the old action does not have the raceway for it to run in. I then put it in a regular LA stock... but had to do quite a bit of dremel work around for the trigger- because it hit in multiple spots and would not set. It's been years and can't remember all the details but at the time the info was that the new triggers were not compatible with it- tried to go aftermarket but no one had one that would work. If a trigger could have been found then probably would have kept it... but as is it moved on. The new barrel screwed right in- but the old barrel nut would not work because it would not screw on far enough to correctly set headspace. Also- stayed with a standard sized round so not sure about opening up the bottom of the action.....