[DonVoigt]

Ed,
If you want a .30 barrel, it can be done fairly easily. I have one or two that could be adapted.
No reason the 9mm would have to use reduced loads, DWM sold old model 9mm pistols with leaf springs and 4" barrels; a longer barrel is heavier and would be fine with normal loads, IMO; especially with the aux. spring in operation.

Ron makes a good point with regard to the receiver length. I would expect that most of Marz barrels were for short receivers.

Does the barrel that is left have the "tab" ? I don't see it.

How about a picture of the frame where the "arm" attaches?

If you are not going to reblue the entire "upper" when done, then , yes have the barrel blued before it is installed.

I guess by "restoring" you also mean to go back to the rear sight on the barrel?