50 mil down ought to do the trick, if you can make it fit; most board houses I've worked with require 25 mil copper clearance and 75-100 mil hole clearance from the edge.
As far as chips fitting side by side, chips with a multiple of 4 pins (16, 20 being the most common) can usually fit. The reason 14-pin DIPs have that problem is because their bodies extend significantly beyond the outer pins, whereas those with an even number of pins per row are usually nearly flush.
Paul, The drawing does not show actual trace width.
Yoda, Those shorted pins above the 5V regulator are for an optional 12V regulator. I agree, the 5V reg should be moved a little right.
Dave, Yes, the holes are close to the edge (aren't we all?).
Right, great questions, let me describe the board.
All the traces between the S-100 and Buffer IC's are 12mil with 13mil spacing. Traces that tie the 74LS245 chip directions to ground or vcc are 8mil. The board is ready to go as a slave board (ie memory, i/o, etc). If you need to convert it to a CPU board, the buffer directions need to be reversed, the 8mil traces need to be cut, jumper wires added. The +5V and Ground traces are 50mil, they extend up the right side of the board and feed every 4th hole (only the top layer is shown, the GND is fed to every 4th hole from the copper side). From these holes, bus wire can be used to feed a row of 300mil chips. The +8V is also 50mil to the regulator, but goes through a short 25 mil "fuse" trace. This way a short will not fry the whole trace and damage the gold plated S-100 pads. The +16V and -16V use 35mil traces and go through a short 25mil "fuse" trace too (I should reduce this to 20mil).
The 5V regulator is at the same location where Andrew placed it on the Unbuffered board, but I agree, it should come a little to the right, say 100mil. Above it are provisions for a +12V and -12V regulator. The power traces reach those pads, but you don't have to use them. There's plenty of holes around it so you can easily install any other IC there around the specialized holes for the regulator. This regulator does not need to move, it will never require a big heat sink... I hope.
The top row can be made like this, but I agree it's a little too close... I think I'll shift everything down 50mil and sacrifice a row on the bottom.
The 74LS245 chips can be placed side by side (even on sockets). I've checked this out with a dozen different chips from my junk box, it works for all of them. I think the 14 pin chips have this problem, especially those from 1970's. I can redo this test and take photo's if that helps?