I'm ordering a flexplate for my 383 turbo motor that I built out of a '97 silverado block with an eagle crank. You can imagine the can of worms I opened when going with the new style block. Now my dillema seems to be how many teeth do I want on my flexplate and what is the difference? There seem to be flywheels in both 168 tooth and 153 tooth that fit 1 piece rear main seal blocks, so which one do I go for?

 

Lower performance cars tended to get the 153 tooth flexplate (305's), higher got the 168 (350's). You could probably use either one, but the starter nose must match the flexplate you use. Inline mouning bolts for the small plate, staggered for the large. Your block should have the tapped holes to use either style, but verify.

This tooth thing also applies to the two piece blocks.

 

Make sure you're using a flexplate that's designed/balanced for your crank --- ie: a 400 crank must use a 400 flexplate (balanced plate), and a 350 must use a 350 flexplate (balanced crankshaft). Since you used an aftermarket crank, it may be balanced, therefore you could use a flexplate from a 350, but that's something to keep in mind - otherwise your motor could vibrate itself to death!

 

I have a 153 tooth flexplate and one of those light (GM/Hitachi style) ministarters

Installing that starter was a dream since I wasn't worried about dropping it on my face

I would guess you could get one of the gear reduction starters and the smaller flexplate wouldn't be a problem unless it actually has something to do strength and not just the starter gear ratio

 

you have to know if motor is internal or external balanced
than make sure it matches harmonic balancer