That surprised me as well...

How small they were inside, that is. They look HUGE from outside but it's almost like a crawlspace inside.

I think you'll find the B25 the same. I have never flown in one but I have been in them.

Generally MOST aircraft surprise me somewhat by being smaller than I had imagined them being. One notable exception, although NOT WWII era... is the C 17... where I had the opposite reaction. It's HUGE. They have different configurations inside but the two I went into had a horizontal deck just behind the cockpit and above the main floor... and I swear, if you fell off that deck you'd break a leg it's so high up.