If you optimize what you have I doubt you will get much benefit from adding the 120kHz UT unless your 40kHz is on the way out. Here are some suggestions for the hardware you have.
With the VPI-RCM, preclean with Alconox Liquinox Amazon.com: Alconox - 1232-1 1232 Liquinox Anionic Critical Cleaning Liquid Detergent, 1 quart Bottle : Industrial & Scientific prepared 0.5% in DIW in spray or wash bottle. Apply about 5-ml to the surface to fully wet and with a light but quick back & forth motion scrub with a Record Doctor brush Record Doctor - Clean Sweep Brush (pangeaaudio.com). Foam - some on the record and most in the brush are signs you are agitating the fluid enough.
After cleaning, perform two rinse/vacuum cycles. For the 1st rinse cycle, do not fully dry the record. For each rinse, apply about 10-ml of distilled water to the record. When applying the DIW, you only need to brush lightly. Note: I am not saying to measure out the rinse DIW each time. But you should measure it out once to eyeball what 5-ml cleaner and 10-ml of distilled water looks like on the record. Many people do not use enough rinse water with vacuum-RCMs.
FYI - the above was developed recently with someone in the UK, and we spiked a cleaning solution of known ingredients and concentration with a high-performance UV fluorescent dye. What the dye showed is that when using blower-style vacuum-RCMs (like the Project), not all fluid is sucked off the surface. Some fluid is evaporated in-place (20-30%), leaving behind cleaner residue. Two rinse cycles (with 10-ml DIW) were needed fully remove the cleaner (and whatever it removed from the record). Also, for the cleaning step, 6-ml was used; anymore and rapid agitation with the brush (necessary for best results) would fling cleaner from the surface. Many people do not use enough cleaner on the record to get good cleaning with vacuum-RCM.
If you are using the same brush throughout, after cleaning with Liquinox and the first rinse, rinse the brush with DIW spray into a sink or bucket.
For your UT tank prepare the chemistry as follows:
First add 2.5-3.0 ml of Triton X100 to the tank. Disposable pipettes are convenient Transfer Pipettes, Teenitor 50PCS 3ml Eye Dropper Plastic Transfer Pipettes for Essential Oil, Disposable Liquid Dropper for Science Laboratory, Lab, DIY: Amazon.com: Industrial & Scientific. Use the pipette to swirl the fluid to get the Triton X100 to dissolve.
Then Add 275-300 ml of 91% IPA. Adding the IPA first will slow down how fast the Triton dissolves.
Degas the tank each day that you are cleaning records before cleaning records or the first batch does not get very much UT. I would recommend a spin speed of about 0.4 rpm and 15 minutes to get 6-full rotations.
Otherwise, for about the price of the 120kHz you can buy an Elmasonic P60H Order 103 3240 by Elma P60H Elmasonic Ultrasonic Cleaning Unit 115-120V - US Mega Store which is big enough to clean 3-records at a time spaced 1" apart, and you get the best of both worlds = 37kHz and 80khz. However, this is a powerful tank, and it will heat quickly so for serial cleaning, a pump/radiator would be required - the book has the details, and if adding a pump add a filter as well.