I have an Arctic Cat M8 skid with custom aluminum drop brackets installed in my 2004 RX1 mountain. It's been so long I barely remember doing it lol!
From what I remember, I used the stock front holes, had spacers manufactured for the inside of the tunnel because the tunnel at the front is wider than the front A-arms. Two spacers to close the gap as worked all this time with no issues.
I had drop brackets made out of aluminum. I measured the distance from the front A-arm bolt hole to the real bold hole center to centre. I used a wooden metre stick and drilled a hole at the one end and a hole at the other end at the measured distance. I put the bolt through the tunnel and through the one hole of the stick. Then I marked the drop bracket with the other hole in the stick to get the exact hole location. I drilled 3 holes in my drop bracket and using the stick it automatically "arcs" to keep the bolt holes precise.
I had to bend my aluminum drop brackets in a hydraulic press to spread them out to allow the rear arm to fit.
There should be lots of threads on this topic from years ago on this specific forum.
If I remember correctly, I think my M8 skid is a 141 which fits the 151 Yamaha mountain track. Not sure what track would fit the 153 skid. The 141 is set back quite a bit compared to the stock RX1 Mountain skid. I installed anti-stab wheels as a precaution and after thousands of kms of flat landing, I have had zero issues.
