I have ported E7s and use Vassco double springs...Not sure what the seat pressure is.. I got them for 83.00
You can buy a tool at your parts store for removal, def take your time and buy a good tool.
I used rope and stuffed 2 ft in the cyl and then brought the piston to TDC... the rope will hold the valve in place while you swap the springs... Be very careful of the keepers... keep track of those mofo's...lotta holes they can fall into...