Torsion Bars

I am adding a sway bar on my 72 duster , with k frame up grade to spool mounts ,, whats the best torsion bar size for handing a 340 . 4 spd , 8 3/4 rear , are the Torsion Bars 892- 893 good enough or should I replace them ? And is there any real difference from any of the 6 cyc to v8 setups as I have a set from a slant six Torsion Bars 890- 891 as they look the same