The hole on the top of the gear box as referred by Vinfriend is the timing inspection hole. The flywheel can be seen through that hole and distributor timing is adjusted using a timing light and manual inspection. Its better if you close the hole using a rubber cap (used in flooring and dicky area).
I have a query regarding the air filters. In all the cars the air filter is fitted inside a plastic/metal housing to protect it from engine heat and extra outside dirt. But if we install a after market performance air filter without any box, the car breathes much better and sounds good.
Earlier I experimented with a car(which came for engine rebuild) and drove it without air filter. The sound was awesome and the pickup increased a lot.
Many muscle cars and trucks from the 60s have open element air filters. These cars have V8s which produce much more heat as compared to our humble M800s. If we make a custom filter box(for type 1) something like this
and install stock purolator filter or a replacement filter, will it increase the mileage and performance ?? Also if I make a custom plumbing and install conical filter will it increase performance and mileage ?