I've built a few of these tilting big basses over the years.
Note how the resonator tubes are situated higher above the frame to bring them closer to the slanted bars. You can scallop off the rim of a tube if you want to get it closer yet to the bar, long as you get the tube's tuning right. And now, with those tubes raised to capture the good vibrations, there's space below the longest tube to lower the instrument a few inches, such that....
..... one may not need a riser to play! I'd say this is still kind of high for anyone under maybe 5' 10" altitude, but now you can use a lower riser. Lower center of gravity for the entire instrument makes it a solid, moveable unit.
It's kind of a challenge to get all the dimensions, and of course an additional rail for the raised back end must be fabricated and attached:
But the biggest challenge for me: How to play those bars with requisite enthusiasm without bonking them off the instrument? No problem with the traditional system of suspending cord threaded through a hole drilled into the bar. But my system of suspending bars on a hefty cord and restraining them with a lighter gauge cord (which allows for bar removal and swapping in F# and Bb bars) isn't enough to counter gravity here. Solution required...
... and here it is. A patch of rubber screwed over the bar channels. Now the bar will stay in place. As with all big instruments, resting the bars on a bed of foam (snake insulation available in hardware stores) minimizes cord wear and tear.
The jury was out as to whether this radically tilted design could stand extended use. But the customer really likes it and after several years there are no complaints.