I sell T56 Magnums and for the most part you need to shorten your driveshaft and add a 31 spline yoke. The VSS pigtail is different and if you are not running a mechanical speedo you need a plug to seal up the port in the trans (T56 Magnum offers mechanical and VSS style speedo outputs). You can modifiy the shifter to get the desired setback quite easily.... or plunk down $300-500 for an aftermarket one.
The 1-4 ratios stay the same... .80 5th is great as you stay in your powerband unlike the .75 factory T56 ratio which is rather tall. The smoothness in shifting is no comparison. I have shifted them as high as 7800rpm in my turbo LS9 RX-7 without issue. It's also putting down 1200rwhp+ thru a 100% stock unit without issue. Car runs 9.30's@163mph launching with zero boost and not powershifting. I have the T56 Magnum also in my LS7 RX-7 and it was a very noticeable upgrade over the previous rebuilt T56 it had. If you don't plan to drag race a standard 31 spline yoke is fine. If you do plan to really beat on it... get a billet yoke. I run McLeod twin discs in all my cars and they work/drive great with super low pedal effort and non grabby uptake.
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Project: 1969 Chevelle, alum 5.3, GTS76 turbo, Chiseled Perf A/W intercooler, Holley Dominator EFI, Davis TC, JRi coilovers, 14" brakes, T56 Magnum. CTS-V Recaro seats!
Coffey Fabrication Nashville, TN doing the fabwork! 800rwhp+/25mpg+/9's@150mph goal 
https://lateral-g.net/forums/showthread.php4?t=52976
1993 Mazda FD RX-7, built LS7, T56 Magnum, Holley HP, Davis Tech TC, 8.8" 3.73 Cobra IRS diff, DSS axles, Ohlins coilovers, big brakes.
CCW 18x11 front 315/30/18's and 18x12.5 rear on 335/30/18 RA1's, 2850lbs
10.31@137mph 165mph Shift-Sector 1/2 mile speed
441ci AllPro headed motor and 200lb weigh reduction in the works....
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