I have a 88' Crx with a rear disk conversion from an Integra and the front brakes hold pressure as I drive.

 

the master cylinder was replaced wasnt it?

you did not space the master cylinder and brake booster pushrod properly.

http://my.cardone.com/techdocs/PT%2053-0001.pdf

 

What that means to you is just add clearance by adjusting the pushrod down in the footwell where the pedal connects. Adding a little bit more free play before the pedal starts actually pushing on the master cylinder will fix this.