This is one area in my opinion where newer doesn't mean better. Those older furnaces were great, and it's too bad they don't make them any more. You won't be able to find anything as quiet and practical on the market today, and I know many would pay a good price to get one. No electricity, no moving parts, no fan, no noise, no humidity, and no CO or CO2 thanks to the outside venting. Low maintenance, too. We consider ourselves lucky to have one that is still in good shape - 35 years old and willl probably last for many more years to come. I will go to great lengths to keep ours in good working condition before I consider swapping it out for a "modern" one full of wires, electric controls and (gasp) a noisy fan. Can I have yours as a backup?
All a matter of opinion and preference, of course.