Hi Fred.
You are correct that having an AM filter would improve the listening experience. I your case though, given how difficult it is to find a filter and the fact that the 301 isn't general coverage, there are limited opportunities for SWL. Unless you really, really love your 301, it might make more sense to get a portable SWL receiver for around $100. something like a Techsun PL660 or a reconditioned Sony 2001D/2010 (my personal favorites). You'll likely spend more than that on a filter to maybe just listen to 40 meter SW at night?
If you're competent with a soldering iron, performing a capacitor/resistor bypass on the AM slot in the filter board might work, but ONLY if you know what you are doing. I have not personally done this mod myself, so buyer beware..you assume all responsibility for your rig if you attempt this.
