I swapped in a 400sb about a month ago and had wicked bad vibes that weren't there with the 350. After alot of head scratching,swearing and doing a grease service on everything possible to no avail, I decided to suck it up and search the site "Search" turned up a previous post where someone mentioned the externally balanced flywheel on the 400sbc. Now, I new about the harmonic balancer being externally balanced. But I never considered the flywheel.(I used the one from my 350) So I proceeded to undo everything I managed to accompolish in the previous 3wks I'll tell ya,externally balanced flywheels must be extremely rare around here.Not one yard around here had one,and autozone was the only option at just under $100 Then while browsing DIY's site one day I found the "engine balance plate". I e-mailed Kert and inquired as to whether or not it would work with a manual trans( it's advertised for use with auto trans.) He said it should but he hadn't tried it. Well, I decided that I'd be the guinee pig on this job and go for it. I ended up having to pull the engine again because the trans wouldn't slide back far enough to pull the clutch assembly and flywheel to install the balance plate.So,after 4hrs labor and $15.75 total cost, my problem is solved. NO MORE WICKED BAD VIBES FROM USING THE WRONG FLYWHEEL!!! The moral of this novel is this: The "engine balance plate" does and will work with a manual trans. I have minor issues with the starter,however, I do not believe the balance plate is the cause. I 'll start another post in just a sec. with those questions. Thanks for listening to me sing the praises of DIY and such a simple,but effective, product.