You'll need something like the Whelen 6EHDLTMK. Here's a post from a few years back where I recommended the same kit for someone looking to replace Code 3 Oscilasers in similar headlight mounts with Whelen 600-series LED lightheads:
If you go with Whelen 600-series lightheads, be sure to order an equal number of 6EHDLTMK. The 6EHDLTMK is a bracket that allows a 600-series lighthead to be mounted in the headlight housing, in the place where the Oscilaser was. This comes as a result of the Oscilaser having its own housing that replaces the headlight bucket and aiming hardware.
Here's a working URL for the 2013 version of the Whelen Lighthead Mounting Catalog:
http://www.mobilefleet.com/_literature_166455/Whelen_Lighthead_Mounting_Catalog
The 6EHDLTMK is listed on page 2 of the catalog, or page 3 of the PDF.
The current Whelen Automotive Warning Equipment price list is here:
http://www.whelen.com/pb/Automotive/PriceLists/01_Automotive_Price_List-18.1.pdf
The 6EHDLTMK is listed on page 7 of the price list, or page 10 of the PDF, and has a list price of $31.50. You should be able to get it from your dealer for about $18.90. From the photo, it looks like you will need four.
It has been a few years since I have installed lightheads using this kit, but please feel free to let me know if you need any help.
