I have a 408 with a lunati crank. I noticed it when I had buttoned it up the front and rear covers that the crank flange was taller. I have a 4l80e trans but my converter will have 3 bolts and not 6. Who makes a sfi flexplate for tall crank flange that's flat for 3 bolts torque converter pattern

 

any flat flexplate for LS that would normally be used with a spacer...can be used here.
Just omit the spacer

All the spacer does is make the "short" cranks identical in length to your "long" crank

Also...it's a bit odd that lunati would make a crank with the long flange...check the stickies for good info showing pictures and measurements differentiating the short from long cranks