Approximately, you will need at least one package of 85x45x1mm to cover all the VRAMs on the front side.
With another package of the 1.5mm thickness, you can cover the rest of the front side. And thus, a stripe of 3mm is required to replace the backplate stripe.
If you have some thermal pads left, you may can put some additional on the backplate, such as areas that are contacting the back of the VRAMs to reach better heat dissipation.