Our dealer made up new blocks for the rear feed chain and handed them out to all customers so we didn't even need to cut and weld. It works great for corn and soybeans that is for sure! I bet this high position would work well for grain too. Not sure what to tell you about front position for grain as we do not plant any.
No we do not put on front drums. I think the reason AGCO likes the rear feed drum raised is to improve the feeding between the two chains. With the rear feed chain elevated to this high position the material coming from the front chain has somewhere to go. They say if not in this high position material hits the face of the rear drum and has a hard time getting started up rear chain. I think we see less back feeding down front chain with this setting-makes sense to me. We've had these settings for a couple of seasons and has never hurt us in either corn or soybeans and I'm sure helped in soybeans. The guys without air reels have really liked it...claim they slug feeder house much less. I can't see where this setting would hurt. Maybe if crop was really light but I bet it would still be fine.
We run grain position for all crops after installing shocks. Grain rear position offers most available clearance under drum when under load. Modifing block the way you describe will give you very similiar clearance but start out higher. Starting out higher in small grains when running heavy tailing return to cylinder will give you alot of trouble starting the flow. Also if you take in some wet dirt from time to time you will want to leave chain down so it will keep feeding over the stuck dirt until it has cleaned off. Reason for shocks was to allow starting as close to floor as posible and then float up with increased volume. Now if you can get by with drum starting out higher you will benifit for reasons Brian mentioned. If you want to basically duplicate stop mod without the cutting and welding then just shim up the bottom pad similiar amount. With this change a sudden feed of material will get under drum better instead of bulldozing into tention drum. This would be most benifitial with feeder housing very low running flex head. Same would hold true for sudden flow of corn but with feeder normally running much higher it likely isn't as much of a factor. There is some chance that starting drum out higher in corn will allow cobs to organize better and roll into concave. Now if you really want some serious capacity out of these feeders then you remove hump at front of rear floor as well as tilt it down 1". At same time tilt down rear of front feed 3_4". This has basically stoped most all feeder plugging. Of course it helped plenty to do helical mods to prevent second pass over feeder concave area and anti-constipation measures for seperator side of cage. Sorry this got so long. I better cut it off now. Have a great day