You can do like i did, i had a hard time finding a good used 360 oil pan for my dart when i was installing a magnum, i didn't know how good the e-bay pans were for fitment or draglink clearance, the MP peice for me was over priced, so i got creative when i purchased a used oil pan that was suppost to be for a 360, but realized after i got it home (dumb me) it was a 318 pan, so i took & cut the rear of the 360 magnum truck pan & welded it to the 318 pan, at the time i had someone weld it up, i was out 20.00 bucks, it works great & doesn't leak a drop, you already have the 318 car pan, just find a 360 truck pan, wether its an LA or Magnum, there very easy to find, a magnum pan shouldn't cost hardly anything & the easiest to find, scout the junkyards.
The difference on these pans are just the rear seal rail, sence the 360 has a larger main cap, the seal is smaller, so all you need to do is measure where you need to make the cut (i used a die grinder with cut off disc), where it lines up to each end, then i cut each end at an angle going down about 2 inches, then straight across from the 360 magnum pan, then lined it up with the 318 pan (putting the piece on the inside), then had it welded. A relatively cheap & easy solution, then just use your 318 pick-up tube (clean it out good).
