UPDATE: i successfully made a properly dummied, fully working disc of Propeller Arena. the dummy file is at the start of the disc and it now returns to the game after you exit the browser, but the gd drive grinds alot loading the index.htm of the browser. too bad i don't have the sorttxt.txt of the gd-r....
i booted it at lba 45000. and i had to hack the maigo.bins and sg_dpldr.bins. do a hex search for " 5C2E0000 " in the bins and change them to " 6EB00000 ". also, one of the maigo.bins needs to be hacked again at another address. i forget where, but its right before the previous instance of 5C2E0000. do a compare of the maigo in the root and in the dp3_us folder. i think the one in the root is unhacked, but i'm not sure. just copy the root maigo.bin to the dp3_us folder.
good luck.