I use a group 34R Odyssey as my starting battery. I bought a group 27F to use as a house battery for a fridge, but figure if absolutely necessary, the 27F could be shoehorned into the stock spot in the engine compartment with some minimal adaptation or fabbing needed. Some have claimed to use a group 31, which is the next size up from 27F. With either 27F or 31, inner side of the battery is would sit pretty close to the alternator and the hot air stream from the fan.
In Odyssey world, the 27F is the "stock" battery for our 4Runners. Used to be the 34R, which is only fractionally bigger in capacity) until they bought Northstar and they consolidated the available battery sizes from both companies under the Odyssey badge. RIP Northstar batteries.

I got the tray from CBI and put a group 31 100ah battery in. https://www.toyota-4runner.org/2722723-post34.html