You are correct on 4 bulb set up . Its been awhile. I belive all your bulbs in the original tail are single filiment ? On your new lights ,Is one of the bulbs a double filiment ? if so ,It would be the running tail light plus stoplight wired like a 70 model. Im' sitting here racking my brain trying to remember the color codes. Brown is always Ground !!. As long as you don't have the brown wire hooked to the hot side of something other than the metal (?) housing you should be able to plug any wire to any blub holder and something should light up. You could get a buddy to turn on things, mash the brakes , turn sigs, Rev light (with the switch on) and find out what wire does what with a test light.
