The 707's family tree is convoluted and confusing but in essence, the "138" bit means that it's QANTAS' shortened (by 10ft) version of the original 707-120, and the B means that it has a lot of the changes and upgrades from the Boeing 720 including a wing glove (basically an extension of the leading edge near the wing root to increase sweep angle), JT3D turbofan engines, enlarged vertical and horizontal stabilizers as well as a small ventral fin.
I'll be using freeCAD because i fucking hate myself (and i'm expecting this to take a while and might lose access to my beloved solidworks. Fusion360 looks equally as janky for what i need to use it for tbh) but i have gotten a wing and a panel line so that's evidence enough that it's possible as far as i'm concerned lmao