This is definitely no substitute for getting it jigged, but there are a couple things you can check. Like any square or rectangle you can check square by measuring corner to corner and comparing those measurements, it's a little tough because so much is in the way (engine, break lines, etc) but you can do it with a regular square and a combo square (or maybe it was just a square and a tape measure, I forget), and a friend (I do remember I couldn't hold the square and measure at the same time). Measure from where the plate that the master cylinder bolts to meets the frame rail to the front clip to the far corner where the shock tower/front cross member is welded to the frame rail. Do left rear to right front, then right rear to left front and compare the measurements. If it is bent with a twist, this will not show it, if you had a perfectly level floor and leveled the main frame rails to it, you could probably measure the height of the front clip frame rails near the shock towers/front cross member. If the frame is bent in front of the shock towers/front cross member, either porta-power it straight or don't worry about it since that just holds the bumper, grille, oil cooler, and the front brace for the steering rack which would have to be way off to even notice in the steering. A friend of mine had the very front end of his front clip bent 6" to the right and didn't notice it until he got out and looked (we just hacked them off and welded new on). Again, none of this is a substitute for having it checked on a jig and if needed repaired by someone better at welding than me:)