Some grinding going into reverse is pretty common. A lot of owners shift into 2nd before engaging reverse. I do. This may help.
As far as the popping noise, that isn't one I've heard of before. That would make me uneasy too. It's good that the fluid is clean, but if it was changed by the previous owner right before you bought it, it may have been to hide something.
I have this terrible vision of a loose ring gear with one of the bolt heads shaved off at an angle on top. When forward torque is applied, it doesn't hit anything, when reverse torque is applied, it "tips" in the other direction and just barely clips something.
A bad vision...and certainly not one based in fact. Just trying to imagine what could causing a noise in reverse, but not forward.
Hope it is something simpler.
Mooso.
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.