Iridium plug for Jim's Billet head?

I found these plugs that are NGK's Iridium IX series that have the proper reach and hex but the heat ranges are 4,5. Will that affect the engine a lot? Are there any iridium plugs that would work with this billet head?

NGK Iridium plugs:
XR45IX (0.06" gap),XR5IX,XR4IX

Specs:
14mm Thread Size, 9.5mm (3/8") Reach, 13/16" (20.6mm) Hex Size, Gasket Seat, Resistor, Solid Terminal Nut, Projected Tip, Fine Wire (0.6mm) Iridium Center Electrode, Tapered Cut Ground Electrode, .040" (1.016mm) Gap/(XR45IX has 0.060" gap)

I am simply giving the specs that the interwebs have provided me. It just says those sizes for gaps. idk if that means they cannot be changed.