If the mill in question is the BP series I or a step-pulley version that has a similar head, the turret won't fall off ........
IF the ram/head are moved to the rear as far as practical; it's just a matter of balancing the weight.
But, taking out all 4 bolts won't do much good if the BP column casting is solid, i.e. no side access door.
The older BPs Series I had a side door that allowed access to the "spider". Even some of the clones had the side door.
I've repaired a few of those spiders due to stripped threads (don't ask how...) but they were all of the type that had the door.
As an aside, putting in a riser can be a challenge with solid columns.
Textron, in its efforts to reduce manufacturing cost made somewhat of a mess of the BP machines
by eliminating some of the features that made BP the machine that it was. And their QC was not up to par.
I can relate personal experiences with problems that came on new BPs once Textron got hold of them.