modding question about HDS U's

I have read many posts about upgrading the LED in HDS Ultimates. In each case the process involves removing the lens and reflector to gain access to the top of the electronics module. There in lies my problem. The U60 I own is one of the earliest lights. It was bought only a few weeks after they first came out. Those early versions did not come apart in that fashion. The reflector is machined right into the body ala arc4 style. So my question is when did the construction of these lights change? At what serial number did they change. Once I know this I can start the search for a suitable light to modify.