Looks to be pine? If so,you could consider using a Hardwood substitute which will be stronger.Inverting the shank will minimise the risk of splitting down the middle,giving added strength.Alternatively,you might like to put another 30lb in your car's rear tyres,and deflate the front tyres to 20lb, as both these actions will tend to raise the towball height,perhaps to the level you seek? TBO (towball overhang,or distance from rear axle to hitch point) and wheelbase will also influence your results.Cheers

P.S The owner of this van must have a huge car,or at least a towbar with a big riser.