Yes dias the 6L6 is a drop in. EL34 adverts will sometimes add 6L6 as an equivalent  and vice versa. There must be a small difference but for all intents and purposes I think they are the same.
If you search pair or quad EL34 on e-bay then same search for 6L6 the same tubes turn up.....even more for 6L6...which then turn out to be EL34.
The EL34 will utilise the "Hazen grid" mod but the 6L6 wont.