The forward sprag does not have an effect on reverse and there are no other sprags in a 60/65/70. If it has 4th it's not the 3/4 clutches as they are applied in 3rd and 4th (one element releases and the 2-4 band then again holds to shift it from 3rd to 4th). Sounds like valve body mods gone awry to me. A builder that would weld up a bleed hole in your application (MILD) is suspect to me.