TGK- if you've not already done so, you might check fordtransitusaforum.com and do some searches for larger tires to see other user experiences with those.
I went a bit larger than stock on my Transit. It's a 2019 mid-roof 148" with the Quigley 4x4 option (which includes a 2" body lift)
I went with LT 245/70 R16 E-rated Cooper Discoverer AT3 tires. I know some go larger but I was also seeing posts at the time about having to modify wheel openings or that the spare doesn't fit into its storage area under the floor. I see some compensate by deflating the spare and/or use ratchet straps to keep the spare in place even though it doesn't fit fully into the storage area. There are also discussions about whether it's a problem to mix sizes (i.e., use a stock-size spare when the other three tires are larger), especially on vans with limited-slip rear differential or AWD.
My first set of those Coopers lasted 54K. At that point they could still pass inspection but were getting loud. I had them replaced just before a long trip last summer. I have about 13K miles on the new set.
The larger tire means the speedometer reads low by about 8 miles per hour (according to my GPS).
