I have lightened SBC cast cranks and had excelent results. The lightest was about 38 lbs. We ran these in everything from a 3000 lb purestreet car to limited late model. Some of these were in excess of 430 hp and they held up better than expected.
First off, use a crank that has seen little stress. We used 305 cranks because they had seen less stress than the average 350.
Drill lightening holes in the journals first, then profile the throws and remove all of the rough casting. As you are grinding thru the rough cast the surface will be shiney. After grinding a little more you will notice that the surface is even better, what you saw as shiney will look kind of grey. Grind all of the surface till you have gotten to good clean metal. When you are satisfied that you have a good clean surface, tape up the journals with duct tape and shotpeen the crank. When it comes out of the shotpeen process inspect it for dull grey areas. A dull grey area will indicate the need to grind and polish more.
When you are satisfied that you have ground and polished it well, it is time to grind the journals. When grinding the journals I would always add some radius to the journal, even if it meant grinding to .030 under. This will add strength. It doesn't leave room for a regrind, but the crank will live it's full usefull life if kept clean. Meaning it will crack before it wears out.
I also like to equalise the strokes and make sure the mains are indexed with the front snout and rear flange.
After grinding the journals it is time for a trial ballance. Somewhere around here I have some notes on how much counterweight to remove for X amount of weight. It changes as the diameter of the counterweight gets smaller. On the 350's with Speed Pro Hypereutictics I could find the lowest part of the rear counterweight and set my mill .100" smaller and mill all of the counterweights to that diameter for a good starting point. It would often take two or three trips to the mill to get close enough to call it maxed out, then we would finish with normal drilling.
Most of the cast piston motors would have about a 40 lb crank and the limited motors with the lightest possible parts would end up about 38 lbs. I just can't understand people lining up to pay 600.00 dollars for a cast crank.
Some of these lasted for more than 2000 race laps on a 3/8 to 1/2 mile track, not counting hot laps and packing the track. Thats comparable to the average steel truck crank.
I had a better way to cut the counterweights than the guy in the link. I took an old dampener without the outer ring and honed it for a slip fit. I would center it on my rotary table and bolt it down solid. I would then stand up the rotary table and bolt it to the mill. Insert the crank into the damper hub and use a draw bolt to hold the crank in place. Install my homemade tailstock with a live center. This way I could rotate the crank while milling the counterweights. I could also rotate the crank and rough in the profile of the throws. I could even index it for radiusing the leading edge and knifedeg the trailing edge of the counterweight, all using one setup. This part was done with a ball end mill and it's a little like etch a scetch, then finished by hand. In the end, I could take five cranks and drill the lightening holes in the journals and rough in the throws and mill the counterweights round, and average about 1 1/2 hours per crank. It's not bad when you have a system and can do more than one at a time.
The one crazy, crank related problem I haven't figured out is the SBF. I had a customer who ran SBF motors in SCCA A Sedan.
Spec motor. 10:1 comp, .500 lift cam, GT40 heads, Edel RPM intake, only portwork was gasket match heads not more than one inch into ports.
We would ocasionaly break a block. Most would split from the cam tunnel down. The E7 blocks were better than the F1 blocks but the E7 blocks would still split after awhile. We accepted this as part of a thinned out casting. We used a variety of crankshafts over the years, one of which was a 302 boss crank for the mule, it actualy slowed the car down as expected, so we felt we weren't cheating. One was the early 28 OZ crank so I could exploit the factory lightening holes in the throws and move as much counterweight as possible inside of the block, a step towards internal ballancing. In the end, the engines with the 50 OZ ballancers and flywheels did less damage to the blocks.
This should have been the other way around. The extra counterweight mounted outboard of the block, should have created more of a whipping motion and flexed the crank more, and I am sure it did from the telltale signs of the wear pattern on the bearings. I just don't know how it could, not affect the block more and crack it earlier. The only thing I can think of, is the extra counterweight swinging that far off of the centerline has some effect on the inertial/cycling loads that are created. I mention this because removal of counterweights parallels this. I have seen Pinto engines with all of the counterweights removed and it would be possible to remove the counterweights on any inline engine and the symetrical layout would ballance it but longevity would be lost. You need some counterweight for a given amount of piston and rod weight. I have no idea how much but keep it within reason.
:roll: 
