I wouldn't use solid stock......tube is much stronger.

I would think the ratio of rear leg to front leg length would be determined by your rockers and the amount of travel on top. and of course the amount of leverage you want....which is also determined by your axle position on the rockers.....oh and the strength of your springs.

When I started designing my girder, I found that the best thing to do first is to determine which shock I wanted, then build around it. maybe you should consider getting the springs you want first, then going from there.

it would also be helpful to know how much weight is on your neck without a front end......that will help with your spring selection. mine was about 250lbs. without a rider.