B300F specs:
Diameter: 133 mm
Length: 390mm
P300RX specs:
Outer diameter 132 mm
Length 365 mm
The B300F is 1 mm thicker and 2.5 cm longer than the P300RX.
I just pm'd LA Jetguy, and I'll see what he tells me regarding his perfomance of his 300N engine vs which ever bypass he is using.