Upgrate Polk RTI8 with Lsi9 crossover & tweeter

Wondering if anyone had any opinions of whether or not modifying my Polk RTI8 speakers with the crossovers and ring tweeters with those of Polk LSI 9 would work. I am not be hacking a pair of LSI'9s but have extra parts already. The 8's tweeters are kind of cheapo overly brite at times for music listening using 2 Audiosource Amp 3 amps (2 channel 150 RMS wats @ 8ohms with Harman Karden 645 AVR) The LSI 9's are awesome speakers with my gear but are 4 ohms and would like to turn the 8's into something close if possible but are 8ohm speakers. Crazy idea or what.
If you use the Lsi9 tweeter and crossover, Bi-Amp with 2 Audiosource Amp 3 for high and Low, Adjust the volume control on the amp3 to balance sound, I believe it will work, Is it sound better? I can't tell you. One problem: is the tweeter fit in the cutout?
IME of designing, modifying and buiding speakers (often with Polk's) it will be a bit of a crapshoot.

The challenges include but are not limited to:

If the drivers have different sensitivities, which is likely, the LSI9 x-over will yield a non linear frequency responce.

If the drivers are different impedances then the LSI9 x-over points will shift as well as change the higher slope to a lower 6db slope, leaving a gap between bass and tweeter output.

IMO, you are better off installing the better tweeter and then upgrading the existing RTI8 x-over with better parts as well as changing the tweeter part of the x-over to accomadate the new tweeter.

It may be fairly easy as the two tweeters (RTI8/LSI9) may be the same impedance and sensitivity. In that case you would simply have to upgrade the parts in the existing x-over.

At the very least you would need a Digital Multimeter, a SPL meter, and a CD test disc with 1/3 octave test tones on it.