The 8 foot 4 tube fixture, and the 8 foot "real" magnetic rapid start fixture was the same price. I just needed 4 ft tubes so I can easily "relamp". This 8 foot fixture itself had to be fed through the window just to get into the room.
You should convert this to F40T12 rapid start. BTW, I love the tubeguards that have the black ends on them. Makes the lamps look older. not much a fan of tube guards themselves though.
The F20 strips in the three bedroom closets at my house have gray end covers. they're shown as the cover pic on my Indoor Lighting album in my gallery. the reason i'm not much a fan of these guards is because they make changing the lamp a lot harder since you can't grasp the lamp as easily to rotate it. Plus it's a tigher fit so if there's not much wiggle room between the two sockets, the lamp is VERY sung againt its sockets when installed.
Yeah, I have some fixtures that can't take tube guards because of how tight the sockets are spaced. I have a few fixtures with a tubeguard, including some of my garage lights (don't want falling glass and they help the lamp stay brighter in the winter). The fixture in my cold room also has tube guards.
my twin rapid start lights from the restore are and example of this. my 1973 light is the opposite though, I had to push the sockets closer together just so the sylvania lamps wouldn't fall out! The GEs are a hair longer though and with the sockets pushed closer together, the lamps are fine.
I have a fixture like that too, even with some socket bracket mods i did on it there's still a small gap between the lamp ends on both ends , the LOA undercabinet lights have the opposite problem, some lamps won't even fit!
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BTW, I love the tubeguards that have the black ends on them. Makes the lamps look older. 
The GEs are a hair longer though and with the sockets pushed closer together, the lamps are fine.