My two prior RVs were both small block carbureted Chevy 350s. Countless good memories over 25 years before purchasing my current rig. They do not have much power but fortunately they usually have good gearing (4.10 or 4.56.) It will almost certainly have the TH400 trans which is a strong reliable 3 speed. That will keep you at about 55 to 60 mph max, but it will probably do 55 very well if it is in good shape and well tuned up.
Even if the dash air worked you probably wouldn't use it because it would take about 15% of your available horsepower to run that old A12 compressor. Set up a generator on the bumper so you can run roof air going down the road, that's what we did.
Any old RV is a commitment, heck any RV is a commitment, but old ones in particular. But they can be very affordable and there is no reason they can not be just as reliable as anything else if they are in good condition and well cared for. It comes down to your skill set, your work area/shop/tools, and the condition of your specific unit. Best of luck!