489 third member large yolk

I purchased a 489 case 3.91 suregrip third member for my 67 barracuda. My question is that the yolk looks to be bigger on the new third member than wHow involved is swapping out the yolk on the new rear? Should I leave the yolk on the new third member and change the u joint on the driveshaft to fit? Please advise on best options.
Thanks,
Lou