Even if you've already made your decision and just need a little hand holding or really don't have a clue, to give even remotely usable or sound advice some or all of the following info is needed;
Spring rates front and rear, or at least size of T bars and rear springs used
Overall vehicle weight.
Weight distribution, will vary with type of motor (big block, small block, slant, HEMI), trans, body style (conv, fastback, wagon) wheelbase, etc.
Rear bar planned?
Unsprung weight, lightweight wheels and tires would require less bar to control for example. 8 3/4" rear about 100 lbs heavier than 7 1/4" for another.
Vehicle use?
Sounds like a neat piece and great addition. On the right car!
If you get it, make sure it's the right one for your type of K frame (stock 68 biscuit, 73 and later spool type, ?) or you'll be in for a bit of fabrication. Don't forget to get all the bushing, (end)link, and mount bits also.