Hi,Jerr. I'm Jim,(new member 70cst/ls1). I did my conversion about 2yr. ago. I used a 700r4 behind the 5.3. I used the 5.3 dished flexplate with the700r4 t/converter and made a pilot extension to mate the converter snout into the crank flange. Because the crank flange in a 5.3 is recesed into the block .400 from the bellhousing bolt surface you can't bolt a manual flywheel to it. 5.3 is the only one like this. 4.8 5.7 6.0 are no problem t56 bolts right up. hope this helps.