Andrew,
I wouldn't recommend the kit from Bud's Benz. Lots of money for many parts that you won't use. I believe you can upgrade your compressor easily to a rotary type with an adapter bracket, and several members have had success modifying their Frigiking underdash units with stronger blower motors and internal mods to get better air distribution. This was discussed a lot earlier this summer, do some searches on air conditioner and similar and you'll probably learn all you need. You might also look into a more efficient condenser, also discussed here. I'd guess you can get the system working for significantly less than the price of the BB kit.
Good luck!
George Davis
'69 280 SL Euro manual