Started my aviation career as a CFII in helicopter. Got my private airplane first but immediately got hooked by the helicopter. Used the CFII/H to build hours as a stepping stone to utility and forgot about the fixed wing side for 30 years. I've renewed my CFII/H every two years online.

Now considering retiring from the road and getting the CFI airplane to hang out at the airport in retirement. I will admit I haven't looked at FAR part 61/141 in years. My question, what is the shortest route to add-on a CFII airplane with minimum required hours. I have a fixed wing PPL with 80 hours and maybe enough hours for airplane instrument rating in my log book but not current as I havent flown an airplane in 28 years.

So a commercial and CFII add-on in the airplane? 

"I will admit I haven't looked at FAR part 61/141 in years."

Better start reading then...

https://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&sid=40760189a03dfea0b501608f33820a45&rgn=div5&view=text&node=14:2.0.1.1.2&idno=14

Soooo you're too lazy to look anything up for yourself but you want to work as an instructor? best of luck to any students you may have.

You will need to get a Airplane instrument rating too before your CFII, likely more time for a Commercial requirements, a new long crosscounty in a airplane.  Read Parts 61.123 and 61.129 very carefully for the most part that spells it out for the Commercial, for the instrument extra requirement are spelled out in the lengthy Part 61.65   You may well be able to combine the rides, but the DPE will charge for two.

You then need CFI and CFII training and another double fee combined checkride.  Read Subpart H, it starts at 61.181

All are doable, just a little more involved than you thought, but not too much.  You did not say where you lived so I can't say anything about training.