The PTO on my '56 dump is kinda picky about when it wants to engage.
I found that pulling the PTO lever into gear as I slowly engage the clutch works well. Spins up the gears, but it's still loose enough for everything to mesh & it pops right in. Altho, my PTO lever is pretty tight & only moves about an inch from engaged to disengaged.

1956 GMC 370 dump " 'Tater "
1970 VW Volksrod "the Black Bomber"
2007 Chevy Avalanche
2020 Jeep Cherokee Trailhawk,
2005 Harley Davidson FLHTCUI

I dig all cars, old and new, whether they were hammered out of American iron, German steel, or Japanese tin cans. Being unable to appreciate them all is missing out on a world of great things.
But thats just MY opinion! :P