Interference issues between the timing chain and the front of the block are easy to fix. Using a grinder and a carbide bit, gently grind away the offending area from the block. There is no need to go crazy here-just grind off enough to provide approximately 0.100 inch of clearance between the back of the chain and the front of the block.
Don't forget the plug just above the lifter valley at the back of the block. You must remove it before cleaning the block. Then, tap the hole and seal it with a pipe plug before final assembly.
Now it is time to turn your attention to the lifter valley. Stock blocks use drain-back holes designed to route oil onto the cam. But after the oil drips off the cam, it hits the crankshaft and causes power-robbing windage. The extra oil on the camshaft isn't necessary as long as your engine is properly blueprinted, so you can make some power by blocking off these holes and allowing the oil to drain into the pan through the main drain holes in the front and back of the lifter valley. Prepare the drain holes for plugs with a 1/2-14 tap.
Do not insert the plugs too deep because they can interfere with the camshaft. Also, be sure to use red thread locker on each so you can be confident they will stay where you want them.
With the other oiling holes plugged, you are now routing all the oil to these main drain holes at the front and rear of the lifter valley. These holes should be screened to keep trash or metal fragments from making their way to the oil pump. Begin by removing the casing slag from around the holes with a die grinder and carbide bit.
You can try to make your own screens to fit the holes, but it's really more trouble than it's worth. Moroso makes a screen kit (PN 25000) that drops right into place and even includes the plugs for the oil return holes and epoxy to lock in the screens.
Two screens press into the holes you've just cleaned up in the lifter valley. If you don't use the Moroso kit, you can also use J-B Weld to secure the screens.