I wanted to have heat on my squareback and I was going to use a BAS header along with stock heater boxes until I decided to go with a Tangerine 4-2-1 system.
One could always fabricate some sort of heater boxes around the header if you needed heat I would suppose.
Getting a vintage gas heater that is rebuilt isn't that hard to do- there is a guy in CO that will sell a complete rebuilt and bench tested unit for $450. The new espar heaters are in excess of $1200 last time I checked, but they do have an almost "bolt-on" replacement for a BN2 in their modern product line.
Stock heater boxes of the higher performance variety from a 411/412 were designed to be used in conjunction with a gas heater, so alone I don't think they would provide you with sufficient heat. Heater boxes from a late bus with the triangle flange would be way too restrictive and also would have the worst tuning characteristics of any possible exhaust system you could bolt onto your 2270.
I ended up finding a vintage, almost NOS BN2 for my square in Canada for only a little more than $200 USD. If you look really hard, there are deals to find. You could always fit a larger BA4 in your bug and do a custom type of setup, as we have done in Shad's fastback, beneath his rear seat, coupled with two 300 cfm bilge blowers.
Good luck!
Take care,
Charles Navarro
LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance