lo po cam dilemma

The 509 wants quite a bit of Static compression ratio, or it goes soft from idle to mid-to-late 2000s somewhere. The saving grace for it is that is is ground on a 108LDA.

The6400 has specs of 288/298/112, with .050 of 214/224, and lift of .444/.466.
The straight up installs, put the intake closing angles within 2 degrees of eachother. That means it will be just as soft as the 292. On the exhaust side, the extra duration here,is stolen from the power stroke, meaning when the exhaust opens there is 6 degrees of energy escaping the cylinder,compared to the 292, and that helps fuel efficiency at low revs,not one bit. And to top it off the 050 specs are in the neighborhood of 26 degrees smaller; thats easily 4Plus sizes smaller than the 292.
So what you get with that cam is big-cam idle with little-cam performance,and if your compression is low to begin with; a dog off the line to mid-to-high 2000s, just like the 292cam.And that's why the 3000TC recommendation, and some bigger gears to help it wind up into it's powerband.

So the big questions are; What is your current compression ratio?, and what are the RV cam specs?
If you cannot answer these two questions, and if the cam is out, and if the engine is in-frame, then the only way to answer the cr question is to pull a head off and measure it up.And the only way to figure out the cam specs, if it has no identifier on it, is to fingerprint it. These are not easy or cheap things for a novice to do.
So the hands down,quickest, easiest,cheapest solution,is to slam that RV cam in and see how she runs.And besides,you already own it. And if you don't like it, it's just the gaskets it cost you to find out. And with any luck you can reuse most of those.
You could check all the specs as soon as the cam is nestled in the block;but that requires a tool investment.And the advertised specs will kinda be a guess cuz without knowing who built it you can't really pick a spec to check to.Some manufacturers spec from .006, some from .008, and I suppose some might try to spec at .002.
-But if you are able to provide Scr and cam specs, there are several guys here that can tell you how it might run with those 2.76s and stock TC.I really hope it works out ok for you.