built 347 stroker, can I swap out the existing cam and lifters for a stock 302 HO roller cam and lifters?

You likely can but if this is a custom-built engine you will likely lose a lot of power because the cam is chosen to match the engine's desired torque curve to make a certain horsepower. Swapping to a different cam would also require changes in timing, fuel flow and possibly transmission programming depending on the other components. Rather than needing to alter all of that I would say to pull that engine sell it as a performance part and look at buying a crate engine that better suits what you want out of the vehicle. Or the other option, which won't alter the idle but would help with the brakes would be to add a vacuum pump, there are a few out there designed just for this issue. Jegs, Summit, even Dorman sell units for this use.