Jacob,
One thing to remember, make all of your changes 1 at a time and by small amounts. All the things you have tried and all the things people are suggesting interact dramatically. You can change the effective spine of an arrow by changing the arrow spine, arrow length, or point weight. But you need to try them one at a time-if they don't work, put everything back to where you started and try something else. Personally, I'd leave length as the last thing I changed-it gets expensive having to use a new arrow each time.
Another thing to remember is that recurves, especially older ones, have a pretty high brace height. If 8" is as high as you've gone, that may not be high enough. Hopefully, some others more knowledgeable than I will chime in.
For what it's worth, I plugged your general numbers into Stu's Dynamic Spine Calculator, and with GT 3555's 29" in length you need 200 gr points (assuming your bow is cut 1/8" from center).