I've been pinning up the belly mower on my B1700 now for 24 years, but wear and tear on the mower brackets has caused misalignment of the pin holes several times, so I had to make some adjustments to the adjustment directions in the owner's manual to make it all line up again. Specifically, as the front link and the brackets it attaches to wear, the correct length as pointed out in the manual doesn't work any longer. So the right adjustment is to adjust this link in combination with the rear lift rods until it all lines up correctly. with the mower touching or almost touching the underside of the tractor at the pin location. When done properly, no jack is needed to get the pins in and out; they slide easily, with just a bit of grease and perhaps a gentle up and down shaking of the deck to help them along.
The pins shipped with my 1996 vintage tractor were atrociously difficult to secure, as they were clevis pins with spring R-clips securing them on the inside. I found some longer pins with spring loaded detent balls near a tapered end and a ring connected to the outer end; I attached a looped nylon cord around the ring and they easily pop in and out now.