Vintage Air makes universal Heat/Defrost/A/C units.
http://www.vintageair.com/2012catalog/2012%20VintageAir%20Catalog%20Final%20WEB%20(Page%2042).pdfhttp://www.vintageair.com/2012catalog/2012%20VintageAir%20Catalog%20Final%20WEB%20(Page%2040).pdfThey also reproduce the MK IV under dash A/C unit that would have likely been installed in 68 on a non A/C car.
http://www.vintageair.com/2012catalog/2012%20VintageAir%20Catalog%20Final%20WEB%20(Page%2048).pdfI ordered the MK IV in Carlisle for our 65 C-body wagon. 20,000+ BTU should help keep that long roof cool. I didn't feel that the in-dash units had enough A/C capacity or I would have gone with one of the above units.
And to answer your question I would be very surprised if a B-body box will fit as in bolt in to a C-body. From what I understand the firewalls are different for A/C and non A/C cars so it wouldn't even fit a non A/C B without modification.
All that being said if you already have a B box in stock, shove it up in there and see what needs to be done to make it work. (I'm thinking a lot
)
Kevin
