The OEM 3-pt seats will work reasonably well with racing seats. There really isn't any special secret. The 3-pt belt will come over the shoulder and seat normally and buckle into the stock receptacle.
The only issue that I had was that the side of the racing seat was a little taller than the stock seat so I had to carefully insert the belt into the receptacle on the right hand side (it had to be lined up just right to go in).
You will find that your butt will drag across the left side bolster and wear rather quickly along with having to lift your butt up to get out over the tall left side of the seat. Nothing major, I had this setup for at least a year and liked it quite a bit.
