Hello Paul,
you have possibly already done this by now - I have only just joined - but to answer your query, it is not too difficult just somewhat awkward.
Remove wipers, and the Plenum, and see if you have the frame to hold the filter in place against the cutout in the firewall (Bulkhead). 2 short bolts. Drop heads do not usually have this frame in place, why would you in fact need it to hold a filter in place with an open air car??? I had to wait some time for a filter housing to come up or to be found when breaking a car. Mine came from Reverse in Notts.
I had to cast adrift the wiper motor mechanism in order to get to the location and then it all goes back in reverse order.
Have fun.
Barry.