Last weekend I bought what I think is a 1979 Marshall 1960A, retolexed in snakeskin. It has three 1979 Blackback G12M25 75z speakers and one 1974 G12H30 75hz. It's been years since I've had a 4x12 and I remember that some changed the particle back boards on newer Marshall cabs to one made of birch plywood for 'better' tone. Since this cab has been butchered with already, I don't mind changing more bits on it. I Googled on past threads but couldn't really find anything conclusive. Who has fitted their cabs with a birch plywood back and what is your opinion of it? Yes or no?