I removed mine on 1316 with instructions from Rich years ago.
Lower pans and rear lower grills go, remove air cleaner, remove rear bumper.
You put a jack under the transmissions , take out the transmission bolt for the mount. then lower the jack for the angle.
Take out the muffler bolts and support bracket and yes from the top if you get it JUST RIGHT you can do it. I had a slight dig mark underneath the rear facia from the curve of the pipe. Its alot easier with the clamshell off, but yes it can be done.
I lovethe heffner pipes, the sound and trumpet ends are special.
Good luck
GTJOEY1314