Original post by: Rick ,
The 3:58 and the 3:42 gears are to close. There will not be a 300 rpm difference. I don't even think there would be a 100 rpm difference in the same gear. The 3:42 will be geared slightly higher than the 3:58 meaning it will run at a slightly lower rpm than the 3:58 but just slightly, my guess is less than 100rpm maybe more like 50-75rpm. If you have to change the rears the 3:42 might be a better option because of your speed, but will only decrease your rpms slightly. I'm with you on the older detroits, got to love them. I'd like to hear more on that 14L series 60 detroit. Keep us posted.