Are they worth the money and effort?
If so, is there an (aluminium)underdrive pulley kit for a 250 L6 1978 chevy engine W/O AIrco? Or are there any V6/V8 pulleys which would fit?
The L6 pulleys are not driving the accessories that fast.
If anything, you could run a smaller crank pulley,but do not run the larger alternator pulley,it probably won't charge @ idle -800 RPM or there abouts.
You would also need to run a SBC damper to run a smaller crank pulley.
I ran the March crank & alternator pulley set-up for my 1997 Chevy 350 truck & it would not charge @ low RPM,plus with it discharging @ idle then going into charge mode as soon as the RPMs would go up ,I believe it caused my aleternator to stop working.Constantly discharging ,then charging,then discharging cant be good for the alternator,,,can it???????????
IIRC,the stock 350 crank pulley was about 8" & the March crank pulley was about 5" ????
MBHD
Are they worth the money and effort?
Not on a street driven engine. Charging and slow speed cooling could be a problem, as well as AC / power steering demands that may not be met.