Hey....
how efficient are yor welding skills, do you have a mig ? i was in the same situation, dad and i are doing a 71 1200 ute, and the rails at the front and middle were rusted out. i have the car on a rotisserie and spun it on edge and it made all the difference.... if you have a pit or a lift it may be possible. i used a piece of 50x50 RHS and cut it on an angle, then welded and blended it all in on the remaining subrail. you could never tell if you had a look...........
if you pm me with your email adress i can send you some pics if you want = )
if you need any other help give me a yell
cheers Daniel