Abraxas - hotrodded Mule - more mids, less topend and compression than the Mule - AIV-magnet
I assumed you meant "less topend and more compression" ?
Crawler - über-Mule - juicy, thick tones, round, but not dull topend and more compressed than the Abraxas - AV-magnet
Actually AV bridge / AIV neck. I find the Crawler bridge to be more of an über-RiffRaff FWIW
@keen007: I don't have much experience with LP Custom, but the few I played were mostly fatter / darker than Standards, so the extra warmth and fatness from the Crawlers might over the top here - Crawlers really shine when you want to fatten up a thin/bright guitar.
Also keep in mind that
1. despite the vintage specs Mules (and RiffRaff) are far from shy... Not as much output as their hotter brothers for sure, but still enough to push your amp, so switching from say Nailbombs or Crawlers to Mules or RiffRaff doesn't require much adjustements to my settings (FWIW when it happens live I don't even bother adjusting anything), and
2. it's easier to filter out highs and add some compression than to remove compression or add missing top-end.
The Mule neck will deliver smooth vocal tones while keeping enough clarity / top-end to cut thru. The Mule bridge is quite bright (not a bad thing in a fat guitar) but fattens when you roll down the tone pot. If you want a bit more punch and focus, the RiffRaff bridge (AV, late PAF / early Patent N° specs) might be a good candidate, and FWIW the RR bridge / Mule neck is a well-known, working and quite versatile combo, or if you want to keep the highly organic vibe of the Mule but with a bit more push and compression (and a bit less high end) you can try the Abraxas bridge / Mule neck as telerocker suggests (disclaimer : no personal experience with the Abraxas and I don't know how well it will balance with a Mule neck).
Now don't forget to ask the BKP team for more advices... They do know their stuff.