Just unpacked the last of the boxes today and found to my dismay that some of my dies have some surface rest on them. Whats the best method of cleaning them up? would putting them in a tumbler be ok?

Wouldn't put them in a tumbler, especially not several at a time.

If it's only surface rust a rubdown with Penetrene and a cloth is often all it takes. Depending on the die brand the result differs a bit, sometimes there is slight residual staining of little significance.

More severe rusting can be attacked with the Penetrene and either 1200 wet & dry or fine steel wool. The latter will shine up most steel dies but you need to make sure all the wool is thoroughly removed or it will promote later rusting.

Thanks Ozzie