I have recently retro fitted a Pivmatic to a Maricat and have found the default shock cord tension makes it almost impossible to lower the rudders from the fully raised position.
Are you sure that you routed the pull-down line OVER the pin above the blade? My 5.0 had it incorrectly run under the pin and there was no purchase angle to allow pull-down of the blade. Simple fix: route it over the pin. I've seen that same pin moved back 2 inches to increase the pull angle. You must be sure that you re-drill the hole so the pin will not interfere with the blade head when it swings down. Otherwise, this should cure the pull down issue. The 2:1 will do it as well but may not be needed. I'll try to get some photos.
If this link works follow the white line around the pin. Imagine moving the pin 2" to the left.
Link to Nacra casting photo 
