Blown Spark Plug -- 2nd Time

[oxfordlexusman]

In my 2000 GS400 the No. 2 cylinder had a previous blown spark plug repaired by an insert. 

After several years this repair has recently blown out. 

There are kits on the market that can repair this type of issue by going to larger inserts. 

My question is .. What is the maximum diameter insert that can be retreaded into this car's head?

Thanks for any information !!

Peter