Why don't you keep your OEM I/S seat and purchase a used I/S then send it to Sargent Seats of Jackson ville FLA. Sargent will modify a stock seatpan and I/S backrest quite reasonably.
About three years back I had them reshape and add their "atomic cell" foam, moved the rise rearward, narrow the front (short legs) and recover both the seat and backrest for the sum of $268/00 including shipping. This seat fits me better than any Corbin or Ultimate that I've ever tried. And you still have your OEM seat if you want it.
I have a OEM I/S seat that looks like crap, but i'll sell it for $45.00 + shipping.
Just e-mail me at
dukenjoey@yahoo.com.