change the cam first mate, but change the lifters at the same time as if you use the old lifters the new cam will wear very quick and end up like the old one

change your fuel filter aswell asits poberbly the original one still

check your breather pipes under the metering unit above the box as these tend to have holes or split as they sometimes rest on the clutch arm of the box and the arm wears through them

check all vac pipes

as mentioned dw40 or brake cleaner when engine is running and if the engine picks up you know you have an air leak

other than that i carnt think of anything else near the gearbox unless you have disturbed the dizzy connection which always snap