lets just take a look at what your rod ratio is to begin with.

b20/b30/b21/b23 stroke 80mm rod length 145mm piton compression hieght 46mm

rod ratio is 1.8 to 1

if you were to keep the same stroke and shoot for a 1.5 to 1 ratio you would have a 120mm rod. the comresion hieght would be 71mm for the stock deck hieght. you could shave the deck to bring the compresion hieght down. but you would be all the way down in the freeze plugs, and have half a water pump by the time you did this.
a 71mm comp. hieght piston would be extremly heavy, and unstable. you could also de-stroke the crank to get to 1.5 to 1 ratio. say you went to a 70mm stroke, you would need a 105.5mm rod. and piston compresion hieght would be 76mm , so once again you will have to have a insanly long, unstable piston. there isn't any way to feasably reduce the rod ratio with a b30.

here are some of the rod to stroke ratios of other cars
http://users.erols.com/srweiss/tablersn.htm