put tube amp on to shelf of a rack

Or, get the Symposium Foundation Rack.  It can support the weight of your amp and there is ample room on the bottom shelf for allowing the amp to breathe and remain cool.  There is plenty of space above the amp that allows heat to dissipate and minimize heating components above.  The next shelf/level above the amp provides plenty of insulation for upward heat from below it, anyway.  You can order the rack to have the upgraded Ultra Platform for the bottom shelf/level which will further provide superior vibration control and best performance from your amp. 
This is a good example for what you could use regarding heat control and sound quality.  However, per your initial question, it still remains that you need to get your amp onto the bottom shelf.  There are other good suggestions cited above on how to do that.

@tvad  wow this is a great tool. I never know things like these exist and they seem come in really handy for scenarios like this. Thank you!

@ieales Thanks for the reminder and pointing me to the fans. Neat! order placed today for dual fan and hope they can keep the tubes and the gears cool!

....an added note; there are wire screens available for 12vdc fans to keep the random finger or stray cable at bay.

Typically 'chrome finish', but a matte black spray bomb makes 'shiny' disappear....but it's a matter of taste.

105 lbs.of toppling amp would require the reverse of a 'clean and jerk' weightlift move to interrupt.  And milliseconds to decide if the medical bills would be worth it. My amp is on a low granite shelf therefore...*G*

First, "AC Infinity", makes a fully programable rack type fan system that you can get with the venting either in the front, top or rear of the units, I have several and have used them at times when testing new transducers I've built with loads only calculated theoretically before testing.
These can be mounted "Under" the metal frames in your rack at only 1.5" thick and move plenty of air. "It is allot of fan and tech. for the price also".. They use a infrared, "Probe" to sense the gears heat and then cool it to your preference OR send an alarm If it cannot keep up. And if it cannot? You definitely have a problem! They saved several amps from melting at a certain point! "Those darn and, (O-So -Pesky), 0 Ohm loads! They are just trying to "double down" into infinity!
https://www.acinfinity.com/component-cooling/component-fan-systems/aircom-t8-receiver-and-av-component-cooling-blower-system-rear-exhaust-17/#product-warranty
I liked their stuff so much I bought a bunch of the different types/models of the fans that they make. Look around the site and you'll see. 
They are very quiet also. Even when the three fan T-8 is all the way up in fan speed it is still much quieter then my Krell, monoblocks!
The Racks you have can be problematic with that much weight. "I own a bunch of those". But I did have a Pass Lab's, X-350 sitting in the top middle position in one rig and never had a problem!
"I believe that amp is 120-125Lbs.". If you watch "You-tube" there are videos from McIntosh showing the unboxing and installation of their larger amps with which they recommend using, "4" , people to lift and then place into home systems. I'm a big guy, but I will admit that If I had tried to first lift from the floor, twist or walk a few steps into a position to then, "Gingerly, lean forward and place a huge amplifier into an fairly exact position"?
 I would probably have destroyed part of my back. As it is, even with two strong people? Certain heavy gear is still a trial simply because much of it is so large and cumbersome, as well as being heavy! But the fella I sold a McIntosh MC-402, that I sold "Insisted" that he could place it into his SUV by himself. He regretted that almost immediately after doing so.