I discarded the front mounting frame because to use it , mean't that the seat rake would make it necessary for the seat to be too far forward , due to the seat back being restricted by my rollover bar . I needed to mount it as far back as possible , therefore more upright so's most people could sit in the car without their knees under their chin
--- less leg room on that side 
I cut elongated holes in the seat opposite the eyebolts which turned out to be 385mm's from the front seat edge on the tunnel side and 410mm's on the kerbside --- basically close to your hip bones but staggered , not exactly opposite each other. The seat wouldn't even push down into the seatpan before cutting these holes.
It was still very tight so I took the curled edges off the sides over the elongated holes for about 200mm's .
The angle of the seatback being more upright now , I made alluminium brackets for each front mount of about 45mm's length. They will have 50mm's washers on the underside. My driver's side front mounts are fitted this way since first build in 1999 without ripping out , even having the odd shunt on track.
Painted the blue gelcoat over with two coats of black to match the driver's side ---- just needs bolting in now once the paint's dry
