You sure have a situation that begs you to add an AIC (automatic idle controller) to help prevent wet stacking. I am assuming the idleing is to run the air conditioner and or heater. With that said, your oil useage and white smoke may be from the injector O rings.
I would change the oil (15 quarts) and use Delvac 1300S, Motorcraft 1995 full flow filter. Then add 3 bottles of Auto-Rx. Run the Auto-Rx for 200 miles including the idleing and change the FF only. At 500 miles on the oil and Auto-Rx change the oil, filter and add 3 bottles and repeat the process.
I would e-mail
www.auto-rx.com and ask Frank if he concurs with this. I know of 8 people that have used Auto-Rx with great sucess on the 7.3 diesel with over 150K when they used the Auto-Rx.
When you first add the Auto-Rx, take the vehicle on a 100 mile trip. You need to do some serious removal of soot and grime.
This is how I would do the procedure. It varies from the published Auto-Rx only because of your circumstances. And remember, this is only how I would do it, but Frank at Auto-Rx is the authority and may tell you to ignore what I have stated.
The reason I said to use Delvac and the Motorcraft 1995, both available at Wal Mart. This FF is good on all PSD's 95 and up.