There are definitely a couple different size filters, and I have a suspicion that the 260 airbox may flow better. That said I have no issues making these guys run good with the smaller filter.
I played with a few different size muffler openings on the last couple builds, and I found with my built keeper saw it fell on its face hard once I passed the line of too much. I should probably make this prettier, but after 3 different covers and gradually opening this one up, this is where I ended up:
This little bugger runs hard, but there's a whole lot more than just a muffler mod going on...
Interestingly, the last three I have built have all ended up as 1 pull starters, as long as you flip the choke off fast enough. All of them have had the squish set between .017 and .020.