I did similar a couple of years ago for the son-in-law's BBQ (LPG to natural gas). The BBQ shops will not sell you the jet sizes unless you're a licenced gas fitter but if you do some homework to come up with the conversion tables to calculate the BTU's generated between the two gas sources you can work out the jet size required.
In our case I drilled the existing jets out to 1.85mm with a standard jobber drill and it worked great, from memory the jet size for the LPG could have been similar to yours. If it's a multiple burner BBQ, modify one jet and try it. If it burns a clean blue flame then you know you've got the gas:air ratio correct.