Oil filter

as already mentioned i'd alter the exhaust, you only need to add probably a quarter inch to the length of the downpipe where it comes down from the manifold. or if you have access to a lathe just turn up a quarter inch spacer to go between the manifold and downpipe with male and female tapers on it. either should do it.
third and simplest option is dent the downpipe for clearance. don't worry about the dent hurting performance either, just watch the 'engine masters' video about denting headers. plus you already said you will be redoing the exhaust in the future so....
neil.