Would a real butcher block be going to far?

Butcher blocks are very unstable dimensionally. If you live anywhere with seasons, you will a very large change in dimensions from winter to summer. Might not be an issue for this application, but you should be aware of it.

I have a 5" thick butcher block about 20" on a side made from white oak on legs so it is equal to my counter height. I changes about a quarter inch between seasons.

On a side note, butcher blocks are made from closed grain wood, white oak in particular is the best. White oak is naturally toxic to bacteria, and will not absorb moisture very easily. The wood is also extremely difficult to score deep enough to allow debris to get trapped forming a safe harbor for bacteria. There was a rash of e coli breakouts when many health departments banned them, and it took a while for folks to figure out that the plastic replacements where less safe than the wood. They can also be easily refinished by scrapping, and a bit of oil.

It will couple well to the floor because of its weight, so some cork isolation pads are probably a good idea. I doubt fancy isolation pads will do much since it will take a lot of energy to get it to resonate. 

Load a tuning app on your phone and hit it with a mallet. With luck, it will be over-damped and not ring at a single frequency. If it rings in the low mid-range (125-600Hz), probably best to not use it on gear that could be sensitive. Our hearing is extremely acute in this range, and these ranges of resonance will have a lot of energy and be about impossible to damp. If it is made from white oak, it will probably ring above 1200 Hz. Frequencies this high and above can be isolated out with some feet under the gear very easily.

When you say old world butcher block are you talking about old growth European hardwood butcher block tips or American old growth maple? 

Keep in mind, work-a-day butcher blocks were never made for their resonance response to low end frequency and mass. It was built to withstand butchering.

You can get mass from kiln dried hardwoods and laminate accordingly but I doubt very much you will hear little difference. I've got a 25yo console I made from birch plywood and also had a solid heart pine cabinet I made. The former a piece of movable furniture, the other a solidly anchored built-in. The latter proved to be no better in sound quality. Both were utilized in a raised frame house vs  slab on grade.

The old butcher block, imo, is worth it for the story you can tell, not for the sound quality.

1" thick x 13" stone slabs on 2x6 framing with 4x6 posts on a concrete floor.

’Bout 6’ long, and I’d like to move it about 12" ’length-wise’.

However, I’d have to take everything off of it.

Remove the shelves (2); move frame.

Reverse the prior procedures.

Not a happening.

no.

Going with really thick B. Block will put you into the same quandary

Locate Carefully.

Rear guard, J

(aka, CYA)

I ordered custom made  (2 shade ) maple blocks from a guy on Etsy. I finished them myself with stain and poly and brass spiked feet for my vintage McIntosh MC30s. They turned out really nice and the whole project was fun to do. I also saved a lot of money. 

My TT rests on a new Boos 2" hard maple block perched on springs. FWIW, low frequency resonances have been reduced versus sitting naked on the rack shelf.