[screamin_c10]

You need to rebuild that 1406. I had the exact same symptoms you mentioned with my 1406. These old fuel tanks have years of crap flaking off into the fuel and it WILL eventually clog up your carb. replace the filter, clean out/ rebuild/ replace the carb, save your money for a 700R4 transplant and you should see 12-15MPG easy.

I'd personally stay away from the 305 unless you want a new boat anchor. If you really want a good low cube small block that is cheap to build and run, look at the original 307s.