Model 445777 0264-E1 Code 051121YG
 
Engine's on a JD 155C tractor.
 
I've got the repair manual for this engine but not the Microfiche MS-6225 or Sales Manual MS-4052. Anyone know what the Top NL RPM should be? My "guess" would be around 3450-3550 RPM. (Not great at guessing)
 
Thanks in advance!

Most engines are rated for 3,600.   
 
Some mower engines are set for 3,400 per the US gov. 
As you may hit and launch a rock while mowing
that 200 RPM will save someone's life..  No kidding... 
 
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Thank you for the info Scott!  Happened across another thread here a few weeks ago  that stated 3,450 - 3,550.  Will stick to the lower end.

An engine that big, agreed, I'd stick with the lower end of spec's.
 
Being on a tractor, you'll likely NOT just let it run, no load, at WOT. 
 
If you need more pulling power, you can always bump it up..
 
Have fun!
 
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It's amazing what one might find if you dig a little deeper.  Going over the parts list (again) for the 445777-0264-E1  Intek 25hp V-Twin I scrolled to page 26 where the replacement engine and short block is listed.
 
Briggs actually added the spec for Top No-Load Speed: 3,300
 
Regardless, all the replies were much appreciated and I'm still planning on "having fun"!