If that’s a Walthers kit, I believe that the number should be 933-3070. I suggest that you contact Walthers to see if they can get you a copy of the instructions if you don’t get any takers here.
i dont have the plans however i may be of some help look at the movie of my bridge moving it usually runs a lot slower than in the movie shown below… look on you tube or look at the model railroader readers videos… user submited videos
walthers lift bridge with very long union pacific ho scale intermodal train.avi
check out the movie of my lift bridge when i assembled it i followed the instructions and everthing went together easily
do not use the switch supplied i just wired the power directly to the motor and i use a switch to raise and lower you can even wire it to a decoder as explained in the kalmbach book dcc projects perhaps use the decoder to get the signals to change
the lifting arms where thay pass thru the slide cut styrene one inch long and thin enough to go into the slide this will stop the slide from tilting and binding on the lifting arms
the balence weight… i glued in 8 oz of lead fishing weights this is a perfect balence to the lift section and the track / rail
glue the track… i used a full length of peco and glued check rails inplace when the glue… epoxy… has dried hard cut it with a dremel cutter