Fuji still makes (3 X 4), 3.25" X 4.25" pack film (10 shots per pack), in two (2) flavors:
FP100c, (100 ASA color) and FP3000b, (3200 ASA b&w).
Still 'produced'...'fresh'...and 'new!' And...at less than one dollar a shot!

Last year (2011-12), Fuji ended production and/or shipped the last of the 4 X 5 pack film.
There will possibly be [some] FP10045c and FP300045b on the market, (at a cost), for another year(?).

The smaller 3 X 4 Fuji pack film fits the Polaroid 405 backs and Fuji PA-145 backs.
These 3 X 4 film packs also fit Polaroid 100-200-300-and 400 series Polaroid Land cameras.
Mamiya also made a Press/Universal style camera that was Polaroid branded, the SE-600.

The Polaroid 405 backs were made for several MF cameras, 4 X 5 cameras, and even some 35mm cameras.
Both, Fuji PA-145 and Polaroid 405 backs were made for 4 X 5 cameras.

For the discontinued 4 X 5, [pack film], only backs made to fit 4 X 5 cameras were available.
Those backs are the Polaroid 550 and Fuji PA-45.

***Do not confuse the [single sheet], Polaroid 545/545i film back, for pack film use.***
***Polaroid film production ended in 2007-08. The 'freshest,' (now ancient) Polaroid film will be six (6) years old.***
***Impossible Project. (No peel-apart pack film). I will let others comment on this product/project.***

Now that you know what kind of fresh, proven, and quality instant pack film is available today, 'Fuji Pack,'
and the available backs and cameras that use this pack film, it's up to you to choose which camera(s) to use.

Marc