my experience is only with the big block version so it can only be seen in that context .
After use - dyno and track time . Plenum is too big for optimum in stock cubes,i run a stock stroke 440 .
Made the same peak power as my M1 single plane but had to jet very rich due to what appeared to be poor signal . This led to very slow 60' at the track though on the street was not apparent .I did add an insert after this , about 10% volume reduction , this helped a little plus fitted 1" 4 hole spacers this also helped . I have since fitted better flowing heads which should see an improvement , will try again at the end of the year . I know a guy on here has run a small block six pack but if I remember he also found he needed 2" 2 hole spacers which helped in power improvements .

Tex