Looks like on a gen 1 the stock dual sump pan (Fox body style) will fit if we remove the cross member and turn it 180. Here's the info.
"...1st gen. Basic Kit for 289-302-351W Fords...
This new addition allows bolt-in installation of the lite-weight 5.0, requires NO crossmember modification, yet still fits under the hood !!! The secret is simply un-bolting the stock front crossmember (6 bolts), then REVERSING it 180 degrees and re-installing it. This causes the center portion that interferes with the oil pan to swing to the rear instead of the front, allowing a stock double sump late Mustang 5.0 pan to straddle both the crossmember AND steering linkage!!! A short oil filter (or 90 degree adapter) is required, but the low placement buys you a lot of room under the hood for air cleaners and such. Lots of room for headers too. With this kit, the EFI manifold from the Mustang 5.0 will clear the stock 1st gen RX-7 hood."
I found it at
http://www.grannysspeedshop.com/