diff between 69 and 71 frames?

[>X<]

i've asked this before, but not in detail, i was looking at the frame on my 7 daily driver today(seeing if i can tak off my turndowns, but there welded, damn) and noticed that my 71 swb has an extra cross member behind the flat bed mount, before the 2nd to last cross member, this cross member ISNT on my 69 frame that i am using for my project, its diff from all teh others, 1 1/2 o 2 inch square tubing, rivited in, did someone just add this on? i need to post a pic of it so yall can see, also my 71 has a huge 1 piece driveshaft,my 69 had the two piece, so it had the driveshaft loop with teh holes and bracket on it to hold the swivel bearing thing, was this an option or something, what dictates what kind you ahve(motor, trans, year, etc)? one more thing, i thought that i didnt have todo anyting to my frame like boxing, but now i'm thinking that a cross member like th one on my 71 wont hurt? any advice, thanks guys