have a cuple of questions

[lifted 75 k5]

ok i have a 75 lifted chevy blazer that has a sb 350 turbo 350 trans and a np 203 case but i want to change the case to a np 205 and change the rearend to an 8 lug and drop the 6 lug but i am sure that i need a new drive shaft and i want to do it all at once so can i buy the new shaft now and it will bolt up to the new rearend or should i wait and have everything ready and measure and get the new shaft made after i install the new rearend and t case