the filter on the cab side of the firewall? not sure I've ever replaced one of those, it's not much of a filter, more like it keeps the big stuff out.
only 1 nipple on the cap doesn't work very well for air circulation.
the hose going to the air cleaner "T"s into another line
there should be 2 nipples on the cap 1 on each side of the coil wire.
1 line goes from firewall to the cap and the other goes from cap to air cleaner
it is to let the distributor "breathe"