Bigger engines are the primary reason for putting MII front ends in classic Mustangs. Bigger means heavier and hence handling improvements are likely offset by worse overall balance. You're up north and close to Cobra Automotive. If I were you, I would go with Cobra Automotive's approach to classic Mustang suspension and handling. You'll be starting from a known and respected baseline instead of winging it. You'll have someone to talk to when you've got specific problems.
http://www.cobraautomotive.com/