I can't seem to find which IPS i should apply for the NES romhack (the rules link to one and says it's not allowed.. which is helpful.. but not as helpful as a link to an allowed one..)

Based on xerox video it seems like it's this version: https://www.romhacking.net/hacks/527/

SuperMegaDav's looks like it's: https://www.zophar.net/hacks/nes/super-mario-bros-13/Super-Mario-Bros-Special--844.html

There doesn't seem to be any gameplay differences between the two but it looks like most people on the leaderboard(same with me, but I don't do RTA) use the one from romhacking, so I'd recommend using it for the most consistency.