yes, absolutely you must elevate that amp somehow. nothing sucks tone out of amps (or drums, for that matter) more than sitting them on the floor.
next, you have to have a great sound coming out of the amp to begin with. i'm a firm believer that tone is in the fingers foremost.......once you get great tone from the fingers, guitar and amp, and it really doesn't matter exactly what you throw in front of it. beyond all, make sure that it sounds good in the room first........if it sounds like crap in the room, it'll sound like crap on tape.
i really like the B1 on amps. i think that's one of its strongest points, actually. between that and the 57, you should be able to get a plenty good recording, assuming you have everything else under control.
no one can tell you exactly how you need to position the mics--you'll have to find that out for yourself through experimentation, but as a rule i generally start with the 57 on the grille, about 1/2 between the middle and edge of the cone, and off axis about 30 degrees and tweak to taste. the B1 i usually stick about 3ft back of the amp (or wherever it sounds "great" to my ears in the room), and be careful of the levels. i guess you could say the B1 is the room mic.
i've also really been digging my RE38 on amps lately.......very fat sound out of it--complements the 57 and B1 pretty well.
also be aware of mic spacing and potential phase problems. if it sounds "thin", flip the phase on one of the mics and see if that helps any.
one of the things you'll notice is that multiple mics on an amp may end up sounding muddy. some of the most classic recorded guitar tracks are actually very thin when you really listen to em, and they were multi-tracked.....meaning that the player has played the part several times and the final mix is a combination of all of the performances. doing this will "fatten" up your guitar "track" a lot more than sticking 3 or 4 mics in front of an amp and playing it once......but it takes a talented guitarist or at least one who's practiced the part so much they can play it in their sleep.
cheers,
wade