install instructions are available from Marlin.com if you arent comfortable with machinging your case go with the 4.0 gears
you still have to take you tcase completely apart, but the 4.0/4.7 might be the best idea
yea, id be a bit more easy using a 4.0 and keeping the case in tact. i guess i could always re-do a t-case from a salvage yard and swap.
