There usually isn't much residual oil on top of the heads that doesn't drain through the return gallies and the only other oil would be in the oil pressure gallies and that will surely be limited. I assume the oil pan was nearly full and with a couple of quarts of gas in there too, it would thin down and seep out of the oil pan gasket, front and rear seals. Gas breaks down the viscosity or thickness of the oil and it will find a way out that the oil can not alone. I think when you pull the oil pan plug you'll find it has much more than the usual capacity in there. Be sure to have a big pan under there to catch it all.
Let us know what you find so we'll know if our suggestions were close.
GOOD LUCK!
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.