lp to natural conversion

[buckup5]

I'm trying to help out a buddy and convert a deep fryer from lp to natural.The input btu is 35000 the pressure at the orfice is 4" w.c. so i think that the valve was never converted properly the first time just different orfices installed the pilot looks normal but the burners are lazy and i'm not sure what size the orfice needs to be.This darn thing was a mess with soot.Go msot all the soot cleaned out. Any help would be greatly appreciated.