c notch on a stock frame

[Matt_ks]

hello, Im new at this restoring thing I bought a 70 snb truck about 4 yrs ago and have desided to start a frame off resto, how ever I have never been this deep into a project before, so here is what I have done to the frame so far...
I bought a 4/6 drop from Early Classic, a 5 hole disk conversion with 2.5 drop spidles, I have been told that i will need to notch the rear frame, so i went to my uncles weld shop and found some scrap 6 inch oil field pipe to weldinto the frame, but I have now Idea just were to make the cut. So this is what i have done in an effort to estimate the spot to cut... I took the springs out of the rear and with the rear end still bolted to the trailing arms, I allowed the frame to rest on the axle tubes and scrabed a line on either side of the tube on the frame... So my question is will this be a reasonable place to make the cut? Any and all help will be welcomed
please help!!


note the pic in the avitar spot is a hope and dream of mine someday.