R105A ARR 15 receiver IF bandwidth question

I have one of these surplus Collins rcvrs and was wondering how to make it a bit more selective. It has a variable IF which makes the normal fixed IF mech or xtal filter mod inapplicable, at least thats how it looks to me (not an RF design expert by any means). There was a brief article in an old 73 magazine that suggested using a Q5er, but no details. I have used Q5ers (ARC 5 LF rcvr used as an outboard IF stage) with fixed IF freq rcvrs, but don't see how it would be practical with the ARR 15. I don't want to have to retune a Q5er every time I change ARR 15 tuning using its variable IF.

Dave Ross has the following suggestion on his website:

"I have an aversion to 'War Crimes' and generally try to stay away from modifications, but a nice addition to this radio might be a 6 KC mechanical filter somewhere in the IF section. In order to preserve the tuning scheme, you'd have to set it up such that when the BFO - CALIBRATE control is off the '00 KC' detent, the entire variable IF setup is still in play - the mechanical filter would be used only when you're at the fixed '00 KC' position. If you try this, please let me know how it works."

I'd like to figure a way of reducing bandwidth that doesnt require me to essentially disable the variable IF in order to use a filter. Maybe there is some sound card genius who can point me to some tracking scheme?

I really like radios with moving parts and motors. This baby speaks my language. I plan to pair it with an ART 13 xmtr. This pair was flown in post WW 2 Navy patrol planes like the P2V5 and 7 Neptunes. Any ideas welcome. I have the receiver running, everything works including the wonderful 10 ch autotune, but it's as broad as a barn door. Now working on getting my ART 13 xmtr running with an orginal screamin dynamotor PS. Lots of things rotating in my shack! Hey, can you call a dynamotor a "solid state" DC-DC power supply/converter?

Thanks for any advice.