The original bolt handle can be altered or an aftermarket handle could be used.
Brownells in the US can supply weld on aftermarket bolt handles.
The 602 already comes with an extended type magazine box which will easily hold 5 belted magnum rounds.
The magazine floorplate is a bit ugly though I reckon.

I don't know what scope you intend using but the Leupold Compact types use a smaller ocular lens than their other scopes and this can assist in obtaining a lower mounting height.
The only problem with very low scope mounting is that it can sometimes make it more difficult to load the cartridges into the magazine.
The mounts need to be very good quality and fit and MUST include some type of recoil stop to prevent them moving along the dovetails and slipping in the rings during recoil.
The Brno has a recess machined into the left side of the rear scope base for this purpose.
Warne make a lever type QD mount system for Brnos but they are most likely made to clear the standard bolt handle and therefore could be higher than you want.