Depending on what events you are planning on riding (you may just want to tool around on open track day) and banking degree aside, long cranks are not very good at accelerating quickly so being "competitive" in a match sprint may be out, the event likely to have you going at the slowest speed on the bank anyways.
With a 31" inseam I have run 170's for as long as I can remember, my brief soiree into 172.5 territory had me feeling like a fish out of water, the most noticeable downside being the acceleration factor. Then again I'm a straight up roadie, not a track guy or TT/ Tri guy. YMMV.
Hopefully an experienced track rider will be able to chyme in, as even when it comes to banking not all tracks are created equal and the degree of banking can vary quite a bit.
It all depends on the angle of dangle when you're on the banking (ie your speed), the height of your bottom bracket and the length of the cranks. Pedals can play a small role in having a quick off down the banking too.
On my very brief experience of tootling around the velodromes at Leicester and Manchester, you're more likely to slide down the banking on your [censored] from going too slow before you catch a pedal on a well designed track bike. Leicester wasn't too bad but Manchester was a bit fecking steep (seemingly around 45 degrees). By default you need a bit of speed before heading around that banking. If you're going fast enough, crank length isn't an issue. Sosenka broke the hour record on the track with 190mm cranks. Got length?
If it's your first time at the track I'd ask a lot of questions. Some tracks require you to take a 'learners' course to get a taste of what's going on. If it's an outdoor track with a non-wood surface then that requirement may not be present.
I think the pursuit guys may be on the longer cranks - I think Boardman used 175's for the "ultimate" hour record in 96. You should be able to pick up a set of shorter cranks pretty easily and I wouldn't be too surprised if there's a place at track meets for folks to post equipment for sale - like a notice board. I'd ask some of the folks who help out at the track the next time you're there where the best place is to pick track specific equipment up from. Just make sure when you buy the cranks that the chainring (if you end up buying a chainset and not just the cranks) matches the pitch of the chain that you're using. A 3/32" chain will not work with 1/8" pitch chainrings for example. If you're using a standard road chain then standard road rings will be fine.
