Robert Frost created a scenario for Corinth 1.01 that covered the discussion on the arrival of Ewell's II Corps, the scenario was called Gettysburg- Change of Plans and included changes in the Union arrivals that also might have happened. Here's is a brief description of the changes that was included with the download.
CONFEDERATE OOA:
• Ewell orders Johnson to countermarch to Carlisle and then follow Rodes. On the morning of July 1st, Johnson’s column is 3 ½ to 4 hours behind marching via the Carlisle Pike. Units are subject to random arrival.
• McLaws, followed by Hood, begins his march to Gettysburg unimpeded by Johnson. They would have encountered Hill’s train, however, so the road is not entirely clear. These divisions begin arriving 9-10 hours sooner than they did historically. Arrival times are random.
UNION OOA:
• Birney’s division of the III Corps is occupying the position held historically by Doubleday’s. They are protecting the Union left flank from an attack via Fairfield. This was a concern of Reynolds and this same anxiety extends to this scenario. Humphreys’ division is to occupy the position along the Emmittsburg Road that will be vacated by the I and XI Corps and will be in support. Sickles has been ordered by Reynolds to these positions and will advance as the battle is joined. A rear guard will be left at Emmittsburg as per the historical situation. The arrival of the III Corps is random.
• The entire I Corps is moving to Gettysburg via the Emmittsburg Road. Marching in its wake, the XI Corps detours to the Taneytown Road and advances in parallel. These arrival times are fixed, not random. Both corps are just off the south edge of the board, and the lines of march have been agreed upon by consultation of the commanders.
• The alternative Slocum exhibits some interest in what is happening up the road. Williams’ division is sent to Gettysburg, beginning a random arrival at 1300. Slocum receives word at 1400 that a major battle has been joined and orders the rest of XII Corps to the field. It will begin randomly appearing at 1600.
All other units arrive at their historical times/places.
If you're interested in his calculations of arrival times you can find the scenario at Brett Schulte's site
http://www.brettschulte.net/ACWCGDC/index.html under Scenarios - 1863 East - Norris-Frost - Change of Plans