You won't need to split the engine off the Gearbox.
You can drop the Diff out (assuming this is a Rod Box) and select 1st and 4th from there.
Take the Flywheel off, Flywheel Housing off and your Drop Gears are right there.
Kinder to your "cogs" too
.... mind, you're also most of the way to swapping the actual final drive 'n all.