Question for fenderwell header guys/gals

trying to fit along that firewall!
There are transitions spot welded on (re-pops available)
upload_2022-6-9_9-7-37.png

as well as the inner FWs....
upload_2022-6-9_9-8-30.png


If i drill inners out how much risk will there be with the frame rails moving? (without suspension under it)
If the K member is still in, I wouldn't expect the frame to move. You can also brace the rails across temporarily.