The only reliable source of information is to jot down your engine serial number and call Cummins customer service.
Also part of the answer depends upon the transmission make/model, you should also have that information when calling.
Just being an ISL/L9 engine does not mean your engine may be safely uprated.
Last I read, Cummins was charging approx. $750 for an uprate with warranty.
2000 Winnebago Ultimate Freedom USQ40JD,
ISC 8.3 Cummins 350, Spartan MM Chassis. USA IN 1SG 11B5MX,Infantry retired;Good Sam Life member,FMCA." My fellow Americans, ask not what your country can do for you, ask what you can do for your country. John F. Kennedy