Not for old timers or those who've done it a hundred times. Folks with plasma cutters and fully equipted shops wont need to waste your time. There's no rocket science, just a look at how I frenched my stock taillight. I made this quick video for anyone who has basic tools, basic welding skills and the desire to french their 49- 51 shoebox tail lights. Go ahead and use it as a guide and improve on what I've done. ...Just click and play Cheers.
My teacher would call those 'tunnelled', not 'frenched'. She always was a pain in the ass. Cheers -- Gary Real joy comes not from ease or riches or from the praise of men, but from doing something worthwhile. -- 
Sir Wilfred Grenfell
Of course there's that other ugly debate: Frenched headlights or tunneled headlights using 53 Merc rings. Boy have I been lead astray....
Looks easy and the outcome looks great! Did you put lead over the weld before filler? Maybe I'm too freaky, but I always try avoid the situation where moisture can attack filler from behind.
I used metal solder. I didnt add that into the video because I know it's one of those concepts filled with heated debate. Who need to add more heated debate to things.
I guess I too am "Old Skool" We called them "Frenched" Head and Tail lights as well as Antennas. Nice video, easy to see every detail...Good Job.