On my '82 the original 185R14 Continental spare fit fine without
wrestling. Since changing to  195 75R14 tires (including spare)
I also have to do the jack trick to get the cover to close.
I looked into the cover and on top there are two metal rods
that hold the tire. If those could somehow be either adjusted
or exchanged one could easily fit a larger spare. Obviously
on the vans which come with 205 70 tires the clearance must
have been increased.

/Martin (and '82 Diesel Westy)