With luck the beam height of the lasers will be equal to or greater than the beam entrance height for your scanners. Then you can just shim the scanner block up if needed using several layers of sheet metal, which you can cut yourself.
But yeah, if the laser height is lower than the beam entrance elevation for the scanner block then your best bet is to take the scanner block to a shop and have them shave it.
The quality of the color blending you see in the output is directly related to the quality of the laser diode drivers. If the analog modulation response of the driver is linear, you should see great color blending. On the opposite end, a pure TTL driver (so on-off modulation only) will only give you 7 possible colors. Most analog drivers show at least some non-linearity, but any analog modulation ability (even from a really cheap driver) is still going to look worlds better than TTL modulation. But yeah, better drivers = better color gradients.
Don't forget that you can also tweak your color settings in software. Often a little software adjustment can largely correct the limitations of a cheap analog driver. For example, if you notice that your orange looks more like yellow, or if your white has a greenish tint to it, these are things you can tweak in software. Some software will also allow you to adjust the modulation curve throughout the range from 0 to 100% output, which is even more helpful.
I had to do some digging, but I found a few examples. (Funny how people never seem to save pictures that show a problem!)
In this post, have a look at the 3rd picture which shows a green question mark being displayed. The dot beneath the question mark has a pronounced tail where the laser did not turn off at the point when the dot was fully drawn. The is the most common example of a "tail", and it can usually be fixed by simply adjusting the blanking offset value in software. However, if you have wildly miss-matched drivers you may need to install a delay circuit to match up the response times. (This was a bigger problem back when we had both DPSS and direct-diode lasers in the same projector, but nowadays nearly all projectors use all direct-diode lasers.)
Another, more subtle example of tails can be
seen in this post. Here the effect is harder to notice, but if you look at the starting and ending points of the white line segments you can see a small yellow tail on some of them, and a very tiny blue tail on some as well. The corrected picture to the right isn't perfect, as there are still a few blue tails visible, but it's much better than the initial picture. Fixing this problem required the addition of the delay circuit I mentioned above.
If you're experiencing tails as shown in the first example (the question mark picture), then you can probably fix that by adjusting your blanking offset. But if you have tails and/or blending artifacts that look more like the second example, then you'll either need to install a delay circuit on each of the 3 color modulation inputs to the projector, or you'll need to replace the laser drivers with ones that have superior modulation response.
But again, before you start pricing new drivers be sure you've tried to adjust your colors in software first, because most modern laser show software includes several settings that can be used to tweak your color modulation.
Adam