Blade, sounds like ericher already has the beam but internet beam sizing calculator would tell you the minimum beam size. If the calculator tells you max deflection allowed for the 5x3x1/2 that's interesting too. I'll bet that beam won't deflect (zero) under 500 lbs, and not much in a proof test. Proof test is pretty easy for small loads like 4x 500lbs, here's a pic where you can use your pickup and a floor jack. I bet one front wheel is near 2,000 lbs which is probably enough but lifting both front wheels would be more like 4,000 lbs. I bet that beam can take 4,000 lbs (but better check it with the calculator first and stop pumping the jack if you reach max allowable deflection). If you snap a chalkline on the beam (unloaded) and leave it stretched when you load it, you can see (and measure) the deflection. <img src="http://www.tractorbynet.com/forums/files/welding/390358-splicing-small-i-beam-together-image-jpg"/> You could even (geek warning) work backwards from the deflection measurement and calculate the proof weight. And then go on the internet and print up an official aluminum sign (for your overhead lifting device) that says "500 lbs capacity, proofed at 2___ lbs per TBN standards." If you proof it at 4,000lbs then someday down the road you can hang a 1,000 lb hoist on it no worries (if 4x is good enough for you).
