tow limit - 1984 Ford Honey with 460 motor under hood

Whether the frame was extended would be determined by the length of the MH. Some do not have frames extended where long ones do. You can look at the frame to determine if has been. Frames on some rigs are extended using a butt weld where others are plated at the joint adding strength.

37 year old chassis ? It needs a professional to inspect the suspension, steering and brakes !

Yes, it will do fine. Brakes may be necessary however.

I had that same RV for ten years, the truck frame stops just behind the rear axle. The RV manufacturer welds / adds a channel to extend the back part of the Motorhome frame.

Often this channel extension is considerably smaller than the OEM truck frame and the receiver / hitch is attached to that. You will want to have a welding shop inspect the hitch for overall capacity evaluation and possibly beef it up with some extra welded brackets or replace it all together with a higher rated hitch.

You will experience 4 to 5 mpg @60 mph that's about 28 ounces of gas a minute! :B

Not to sound sarcastic, but there are so many variables, not the least of which being it's an almost 40 year old rig, with no supporting information provided, that it's virtually impossible to answer.
Furthermore, if you're needing to ask that question, your knowledge of vehicles and towing, in general, is not conducive to successful road trips in an old vehicle that will be working at high duty cycle.
Theoretically, a little moho like that with a big block and a C6 (even an anemic 80's model) has enough juice to pull a toad, no problem, but again, there is so much more to your question, you, yourself need to analyze whether the moho is mechanically safe and competent to tow and stop the extra weight and almost as importantly, consider where and when you're towing.
IE, cool weather, in Illinois is far easier on the tow vehicle than say 100degrees in the middle of summer or pulling a 6% grade at high altitude.

Good luck with your venture!

It certainly will, and will probably affect your gas mileage by only about 1 mpg.

Instead of 5 mpg, you'll get about 4! 460's LOVE the gas!!

It should do just mine!
It has three speed automatic which will make it a gas hog along with 460!