cleaning transmission cases

[FED 387]

Any suggestions on how to clean 1000's of miles of road grime oil/grease and crud off the outside of stock aluminum automatic transmission cases??? I just picked up several and want to get them cleaned to do a race trans build up----Can you clean them like a iron block that is bake them and then blast them or will this ruin the machined passages in the case???? I,m sure the trans shops have a way of cleaning them just need to find out how or what they are doing---Thanx Comp 387