The Executive and the specific Roadmaster chassis it rides on, are a great combo. You should be very pleased with this towards the top of the food chains of mere mortal coaches:)!
One thing to ask the owner, and review repair/maintenance records that I hope they will have for you, is the EGR. Not a knock on the ISX, just the nature of the beast as far as that generation of engine smog levels are concerned. And that specific ISX, is not one of the newer engines that Cummins did have a design flaw on - and while helping some, really did not step up to the plate as they would have culturally had done just 10-15 years ago to correct their design problem. So I believe you're safe as far as the previously mentioned ISX problems. I'd as about the Ugly Fix, see if that might have been added to your engine. If not, way down the road (I mean get the deal done, do whatever you feel needs to be done when you get it on catch up maintenance, and any cosmetic or interior modifications you may want to make it your coach. THEN GO USE IT FOR AWHILE AND ENJOY!) look into if that specific engine would benefit from the Ugly FIx.
https://www.theuglyfix.co/index.html
You should find the combo of the ISX525 and I believe ~1850(?) lbs of torque coupled to the Allison 4000 to be a sweet combo to drive. Especially at 40' vs the heaving 45' coaches. More then ample power to weight ratio. Mountain downhill grades, with the two speed Jake Compression, should also be a non event. Heck, with that braking HP, you may find yourself needing to add some speed at times:)!
As you learn to drive it, and get a fill for it, think about how you want your Jake Brake to work. I'm not certain if Monaco of that era choose to have it go into 4th gear to start, or possibly even 3rd (Other Monaco Executive coach owners will help you on that specific.). But I know many Country Coach owners, which starts out in 4th gear, had this reprogrammed to select 5th gear to start off with. This give you the option of say rolling down a gradual grade at 60-65 without needing to use the brakes. Heck with that displacements braking HP, you might not even need to engage Low Jake. (Midi size blocks, like my ISL or say a CAT C9, with much less size displacement to add braking HP - will often use 5th gear Low Jake to coast down longer lower percentage downgrades.) You may find that you like things as are, and for sure, it is all about what you like. The advantage of 5th is, well, it lets you use 5th as an option with Jake Braking - and you still have the option at the push of a button to go down to 4th if needed. Where as if you start out in 4th with Jake on, the speed and RPM combo may not be what you want. Perhaps with that coach and that drive train rolling along at 50-55 vs 60-65 MPH that would be available with 5th gear.
Enough from me:)! Go finish the process, and get familiar with this coach as is. Have fun, be safe,
Smitty
