Question for frame gurus. OR How smart are you?

[Primered_69]

Background:

I have a 1969 lwb frame with leaf springs in which I relocated the gas tank into. There is a crossmember before and right after the tank. The first crossmember has a bracket to hold the rear brake line.

I also have a 72 frame with leaf springs I am swapping over to. However there is no forward crossmember in front of where the gas tank will be. Instead there is just a small tab where the brake line attaches to the frame.

Question for the experts:

Do I need to swap out the crossmember from the 69 frame to the 72 frame to still be able to use it with the blazer tank or is this unnecessary? Will the Blazer tank slide w/o the other crossmember there in case of an accident? I already took out the spare tire thingymijiggy.