I think 8hr tempo rides may possibly make you an exceptional case. Personally speaking the longest race I'll do is 120km, you don't need to train your gut for that. If I did 2hrs + on a turbo I'd be minded to eat normal food (dates, nuts etc). You could even put a lovely little spread of food on a plate next to you because you know, you're inside on a turbo, rather than struggling to get something down mid-race hoping that someone doesn't attack before you've finished chewing/swallowing.
Are you going to be eating dates and nuts during your event? If so, great. If not, there's not much point spending your training time eating food you'll not use during your events.
I think 8hr tempo rides may possibly make you an exceptional case. Personally speaking the longest race I'll do is 120km, you don't need to train your gut for that. If I did 2hrs + on a turbo I'd be minded to eat normal food (dates, nuts etc). You could even put a lovely little spread of food on a plate next to you because you know, you're inside on a turbo, rather than struggling to get something down mid-race hoping that someone doesn't attack before you've finished chewing/swallowing.