I think the biggest time difference is using the b-t-b spell acquisition rules in core/complete.
Not Rappan Athuk, but I ran a WB campaign in my own mega-dungeon that resulted in a lot of character deaths and it was not that big of a deal having the players rolling up new ones at the start of each session. I allowed liberal use of meatshields also (we had 2-4 each session), so that helped cut down on the frequency of PC deaths. After 20-something sessions the survivors were up around 4th-5th level.
I've been thinking about starting my next campaign with 0-level characters, à la DCC. Each player gets 4, each of which take a minute or two to roll up, and you expect some or all of them to die. When they do, roll up some more, but if they survive that first foray, make them 1st level and keep moving. There are some decent 0-level PC rules in the back of Pete Spahn's Dolmvay book that could be adapted.