[MylilBowTie]

They have 3 and 2 freeze out plugs on 400 blocks. I would try to get the suffix code off of the front pad on the block under the alternator area. I would also take the valve covers off and see what kind those are as well. The harder of all of them is the casting stamp in the main rear on the driverside. Using all of these will get you a pretty good idea of what it is.

If you really want to know what size the crankshaft is you can pull the oil pan. The crankshaft if it is a gm or maybe even aftermarket will have a casting number also.