This comment is only on the flywheels. The Mark IV 454 is externally balanced, and requires a flywheel that has the counterweight. This is different than the Mark IV 396 & 427 which are internally balanced.

If I recall, the small block 400 is also externally balanced.

The flywheel size will then also determine which bellhousing is used.

Lots to consider George!

Two different diameter flywheels which take two different starters. The 168 tooth flywheel takes the diagonal bolt starter, the 153 tooth takes the starter with the bolts perpendicular to the block.

The 168 is for the 11" clutch, the 153 takes smaller, 10.4" (often called 10 1/2"), or the 10" clutch. You can even go smaller than 10" on that one but obviously you won't.

As mentioned, you need the one that is balanced correctly. The beauty of it is, you can bolt a 6 cylinder flywheel on any small block (except 400) and any big block (except 454) if the the flywheel is from an 85 or older engine. 86 and up is a whole new game, the crankshaft with the one piece rear seal takes a different flywheel.

To give you an example, when I removed the 3 speed in my 66 and put in the 4 speed, all I did was remove one trans and put the other one in. I never even removed the bellhousing. When I put the 427 in, I may even use the 283 clutch and flywheel because I know it bolts on to the 427.

Also, you have a Muncie, correct? Is it a coarse spline input (older Muncies) or a fine spline (later Muncies)? You will have to order the appropriate year of clutch to go with the trans. As well, we were just talking about this yesterday, the bolts that hold the pressure plate to the flywheel are a special bolt, which is discontinued from GM. They were the same for many many years so if you know someone with a vehicle they are parting where you can get the bolts, grab them. Otherwise you will need to find someone who sells them in the aftermarket.

Also two different bel housings . One for the 168 tooth flywheel and one for 153 tooth flywheel. Then there is two different stagered bolt starters . The aluminum nose one for automatic the cast steel nose one is for the 168 tooth flywheel bell housing . 

-- Edited by Beaumont4008 on Sunday 14th of October 2018 05:52:59 PM

Also, I think that the Gen V big blocks and Gen II small blocks with a one piece rear main seal have a different flywheel than the earlier Gen IV big block and Gen I small block.