I've got a CZ .458win in for a re-chamber for the Lott round, however I have read that "not all CZ's with feed Lott soft point from the magazine"

If this should be the case with my rifle, exactly what needs to be done?

I will defer to others on the fix, but I will be surprised if there is a feeding problem. The magazine and action length for the CZ Lott and Win Mag are identical. Additionally, given the length of the CZ action I would not expect that the modest additional length of the Lott will create a feeding problem.

Ditto with what Mike said.

Dirk