Internal speedo drive gear change

[badmts]

I have determined the drive gear I will need is 7 tooth and the driven gear will need to be 20 teeth -now how hard is it to get it inside the transfer case. 1994 Mazda B4000 4.0 5spd button on dash(1354?) Please don't say "it's super easy,just pull back clip swap gears and you are in business"-its the one that turns the easy one from INSIDE the case that I need to change. If you have done this and the answer is pull case/split case reinstall then oh well thats what we will do BUT if you know a cool trick to leave case in place and beat the flat rate PLEASE let me know