I wanted brighter bulbs in the rear also, but never liked how LEDs turned on and off so fast when compared to filament bulbs. LEDs looked too much like a sign flashing on and off. I found Brite Bulbs from Ron Franciis Wiring. These are filament bulbs but the difference from standard filament bulbs is amazing! Even with the 66 "eyebrows" covering the tail lights, they light up like a new car. I have been using them on all my musclecars and have many friends who have converted after seeing them.
You do need to get a heavy duty flasher, but these are cheap and available at any Autozone, NAPA etc.
If anyone is interested, here's the website:
http://www.ronfrancis.com/departments.asp?dept=24
Jim