Old Spec Billet Flywheel: 28 Or 50?

[cw50]

I just pulled my old spec billet steel flywheel out, been in there for 10yr (35k miles)!
Since the machine shop got my parts back then, I couldn't confirm the balance (asked for 28oz) as they assembled it. SO... is this a 28oz flywheel (assuming yes? note there are 4 missing slugs in the lower right corner):

Replaced it w/a new Fidanza AL flywheel, spec 2+ and getting some vibration between 1500-2500 rpms. Trying to diagnosis the vibration as I put the smaller 28oz weight on the Fidanza. Balancer is an old SFI Pioneer.... Revs OK and idles ok, maybe some vibration letting off the gas though.

 

[CarMichael Angelo]

5.0 engines have always been 50 oz imbalance engines, early 302's and 351's have always been 28 oz.

 

[Noobz347]

Is there a part number visible on the flywheel?

 

[Jason 302]

Unless you have an aftermarket rotating assembly, stock imbalance is going to be 50oz on a factory 5.0.

 

[General karthief]

What year is your block?

 

[cw50]

Don't see a part#, the engine is custom: B50 block, 331ci. I asked for 28oz when it was built, all I have is this:

A quick idle test appears to be fairly smooth, will try revving tomorrow to narrow down if it's d/s or just engine side.

 

[General karthief]

SFI thats a safety certification class number. Racing rules stuff.
I think, I bing'd it, like Google only different.