Andy, those cross shafts aren't any better than stock and more important they will do nothing as it relates to making this car work.
That said, there is no one posting on the net that knows better how to make these cars with small tires and stock/aftermarket/bolt on suspension work better than I. Further, there are only 2 other Chevelles and 1 Buick GS in the country last I knew or cared that are on par with my former car and they belong to Kevin Borgstrom '69 Chevelle B/SA , Ralph Landolfi '71 Chevelle B/SA(if he hasn't sold the chevelle yet) and Jason Line '71 Buick C/SA and what do they all have in common...they all run front and rear suspension kits designed, built and sold by Alf Wiebe and only one, the heaviest and least geared had 60 footed 1.28.
IF you want your car to work like mine and theirs, he's the guy you need to speak to. Do it right the first time. There is no bolt on suspension kit/parts on par, no mind better.
Be advised, that even with the best, the end user still needs to tune the suspension and chassis to achieve the results I have which becomes evident once you know that the chevelle in the other lane in my video below also has the same suspension components as my car, going down the track with his front wheels on the ground at 10 seconds in while my car which btw weighed ~ 180 lbs. more IIRC is still carrying the wheels.