I am a firm believer in using 1/8 scale parts to make a larger scale vehicle:
http://www.rc-monster.com/forum/showthread.php?t=26979
http://www.rc-monster.com/forum/showthread.php?t=29657
As for 24mm adapters - you can easily use 23mm adapters wrapped with aluminum tape to run 1/5 scale wheels:
http://www.rc-monster.com/forum/show...=26979&page=12
I think using the d8t as a starting point could work well - it's easy to stretch the truggy platform. I'm partial to the Muggy/LST2 platform and its strength and durability as you can see by my threads - it has worked very well for me.
Keep us posted.