|Front: The strongest point is under the engine subframe. The jack may also be placed under the structural member between the subframe mount where this member is reinforced directly behind the engine subframe mounting bolt.
Rear: The strongest point for jacking in the rear is under the differential. The jack may also be placed under the structural member directly forward of the rear lower control arm mounting point where it is reinforced.
Warning: Placing the jack anywhere else under the this structural member will crush it and weaken the integrity of the unibody structure.
Improvement: It is possible to reinforce the structural member enableing placement of a jack anywhere under it. To do this a hat shaped section of hot-rolled steel of at least 10 guage should be constructed.
The diamensions of hot-rolled plate are: length=38", width=6 1/2". The width of the inside of the hat must be 2 1/8" by 1/1/16" minimum in order for it to fit over the structural member. The options for mounting it are MIG or TIG welding, poprivets (recommend 3/16") or self-drilling sheet metal screws. I would recommend at 8-10 rivets or screws in each flange of the hat.
I have jacked my Jensen at the center of the reinforcement without any deflection of the floorpan. It also looks nice and precludes anyone from jacking your Jensen and damaging the struture.