My name is Marc Duclos I'm just try to get a straight answer on what flex plate i must use. I would like to first say I am 46 yrs old and i always had 400 turbo tyrannies. I'm a truck guy. and i have a project that has to get finished. I have a 1986 Chevy four Dore dull 4x4 . And I just had the 400 rebuilt and i bought a ht 383 from crate depot. I never really understood why crate sent me the engine with a 12" flex plate with a weight on it. My sails men told me he could get me the 14" one for my set up. The question is My sails men said to prevent a vibration the crate ht 383 is balanced by the 12" flex plate. and because it has a one piece rear Maine. And he said not to put a after market on this engine. The tranny shop that did the work installed 99-761 and I matched it up with 14088761 under gm parts. I may seem to be a warrior but if the 12" is for external balancing then dose the 761 flex plate do the same thing for us or do we have the wrong flex plate. I got two Traney shops that I use and one is out to lunch and the other got my truck in September and i towed it back to my finishing garage last week march 5Th. I gave the trany guy plenty of time but now we need the truck. I need to no if a 400 turbo fully rebuilt with a empty torque converter should be filled with the carte ht 383 engine running for the first time with the 14" flex plate #14088761. I'm ready to take the trany out and do it my self like I alway do but before I get ahead of my self do you have any suggestion.