The crossmember will be the same, just farther back. I think the bolt holes will be there. You won't "need" the kickdown switch, but for automatic shifting you might like it. Without it you'll have to downshift for passing etc...
You really should have the convertor inspected & cleaned before installing on a new trans. If it's not an expensive race unit, I'd replace it. May have debris from th350 failure in it that will ruin new trans.
Johnny