A500 rebuild. Removing lockup?

Contact one of the performance converter builders, give them all information they ask for, and see what they recommend for stall for your application. You might want to ask them if they build "DUMMY LOCK-UP" converters. The lockup piston is removed.
If you're going to get into the OD section to see what it's like, remember that there is heavy duty coil spring in there that must be carefully removed. If my memory serves me right it's compressed to around 700PSI.
You might want to check the tooth pitch on the OD planetary. Chrysler upgraded it from 22.5 degree tooth pitch to 15 degree pitch in 1996. There were issues with the early design and that was the reason for the upgrade. There's a kit that includes the 3 pieces for the changeup, the OD sun gear, the OD planetary and the OD ring gear that is available. You would be able to get that from your area Transtar outlet. Another upgrade in the OD section is to change the OD sun gear thrust plate and bearing. Again comes as a kit. There are other upgrades that the parts company I worked for sold that virtually all rebuilders asked for when they were doing the A500. Trailbeast and Rusty can give you their insight as to what you will require.
The attached PDF shows a breakdown of the OD section and the areas I've mentioned.
Don't let price be your only guide, and "Do it right ONCE" JMHO.