2.45s 8 1/4 swap..

i have an 8.25 rear end in my valiant, but i want, scratch that, NEED new gears. i understand that i have to get a whole new piece to swap higher gears because of the machining to put 2.45 gears in it. i would just buy a new chunk, but i cant swap just the center of my rear as it only has a removeable inspection plate and everything else is one piece. what can i source an axle from, or what are my options to get a better set under there? 2.45s are the only reason i havent hit the 1/8th yet to get a base time. what is it in the rear that has to be changed to run numerically higher gears?

thanks, jeff.