Rick,as Andy has already mentioned,if your cab's reasonably solid,you should be OK.
If,however the cab has rot around the floors,cowls,rockers etc, and I assume by the fact you want to brace the cab,this might be the problem,personally I would re-fit the doors,set the gaps as best as you can and THEN brace the cab.
That way when you refit them after welding the cab,they should still fit the aperatures.JMO
