I like the way you used the Hi-lift jack for the headrest, too.
I take it you plan on putting your ex in the back??
Sorry, just funnin' with ya.
I wouldn't use wood to secure the seat- Always think worst case scenario:
What's that wood going to do in a crash, and where's that jack & the rear passengers head going to go when you get rear ended?
You've got a good idea there - free up some space while keeping a third seat, but you're not going about it in a very safe manner...Keep us posted if you get something more secure