57 frame restoration

[candyx]

I'm about to pull my frame out of my 57 3100 ,i have the parallel 4 bar mocked up.I want to box the frame rails front to back add the IFS which i have been learning towards the No Limit Engineering ifs and the frame cross member from Progressive Automotive.My question is should i just seporate the frame and box the rails then reassemble the frame with the new ifs and cross member or keep it together while i do all the changes and remove the old cross members as i go? i plan to weld up every hole in the frame rails that is not in use so it doesn't look like swiss cheese.Then the frame will be powdercoated which leads me to another question,since the rails will be boxed and open on the ends i doubt the powercoater will be able to coat the inside of the rails.Do i need to worry about the inside of the rails rusting or should i try to coat the inside of the rails with something after the powedcoat is completed?