You could try the old see-saw method in trays of chemical. We used to do that in ye olden dayz. Pre-wet the film by see-sawing in a tray of water; then developer; stop. Fix. Total darkness, of course.
I was 11 the last time I did this - with 616 film.
Sorry, you cannot borrow my Dad, to show you how :")
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2
Planachrome - are you processing this for black and white? If doing for chrome, then my advise might only be for the first developer.
I have some long frozen mid 60's era ferrania pan 120. It was around 25-50 iso new , and now is ISO 12. It takes 18' in d76 68F to get a full range negative, and that is for a day or two old latent image.
So for your old film, don't be afraid of going 200% of the 'recommended' development time as a starting time.
I actually heat the developer in the microwave to reduce the developement time to around 5-6 minutes. I measure temp in, and temp at 5' and figure out how much longer than 5' I think it needs to counteract any cool down. I find the paterson tanks keep the dev reasonable warm with minimal drift over 5'.
You may want to see if you have any old 'green' safelight filter, and try develop by inspection after 10 minutes to see what the image is doing. There should be very little un-developed to fog if you only turn the safelight on for a few seconds, even without use of a de-senistizing dye prebath.
Stand in the dark developing with the daylight tank so your eyes are sensitive to the dim safelight output. Look at the emulsion side; the base will be all milky into the film is fixed.