I've got a theory as to why the J-35 doesn't retractable luneberg lens: the area from which the J-35A's one pops out is occupied by the buffed up tailhook on the J-35, and they might have just opted to use a removeable one rather than find another location to have it grow out from.
I've also noticed that the EO sensor (I think) bulge on the belly is below the right intake for the J-35 and under the left intake for the J-35A.
Please excuse the watermark, I've had people take & post my photos without consent and unfortunately had to resort to this.
View attachment 159335