Yes, it can be done! I dood it!
The subject car, along with a 6603-107 LTI gi-raffe head from the Train Tender.
The problem is obvious: Note the placement of the locking lug of the original (top) and LTI (bottom) gi-raffe heads. As installed, an LTI head will not lock in an older model 3376/3386 car.
Two views showing the newer LTI head installed and resolutely declining to lock, as there ain't no floor there nohow.
Note also the homemade compression rings on the actuating lever. Since compression rings are scarce on the ground, I substituted 1/4" aluminum tubing, which works satisfactorily (but which will require replacement after extended use).
"Scrounge" is the modeler's friend. This chunk of plastic came from a discarded parts tray from work.
At this point, Shop Superintendent Norma B. Kitteh showed up to make sure everything was in order, and to get a nice scritch on the head.
Two views of the latching plate in position. At first, I tried JB Weld...
But when that proved unsatisfactory, I drilled a couple of holes and secured the locking plate with sheet metal screws.
The gi-raffe neatly locked down in place. One drawback to the LTI heads is that, with the head down and locked, the latch is inaccessible under the actuating lever. In order to unlock the giraffe, you can either pop the latch with a small screwdriver (recommended) or move the head to the giraffe's right until it unlatches (works fine in a pinch).
The 3386 reassembled and ready for service!
Two slightly different views of the 3386 in service with the new Gi-raffe Train caboose. If you open these images side by side and cross your eyes, it goes 3-D on you! 
Hope this proved informative!
Mitch
