Ideally the panhard bar should be parallel with the ground when the suspension settles to ride height. It can stand a little "off kilter" without ill effect. Even if you put a complete engine in it still wouldn't simulate full front weight as you won't have anything for coolant, oil, loaded fuel tank (yes, even though it's in back, a portion of it's weight transfers to the front), and everything else that goes in/on the car.

P&J designs the bracket you're asking about to be the correct length for the typical 4" dropped axle, with reverse eye stock thickness spring, mounted to a Model A style front crossmember arrangement, so you shouldn't have to modify it if this is what you're doing.

In addition to the comments above, when assembling and disassembling the front (or rear for that matter) spring it's advisable to use a large C-clamp (or similar) when installing or removing the center bolt nut. Lots of stored energy in a compressed spring.