I’ve come to the conclusion that the MegaSquirt controller, as built, will not hide anywhere on a 1982 Maxim 550.
At this point, I have seem to have three choices.
Switch to MicroSquirt; in the long run, probably the best idea. The MicroSquirt is pretty much intended for motorcycle use, being small and sealed. It is also $400.
Repackage the controller I have; not a terribly bad idea. There is a lot of wasted space in the box. It could be a little thicker than half of what it is now and that might get it into the “trunk”. I’ll still have to find a place for the (as yet unknown dimensioned) fuel pump and all those relays and such, but maybe that won’t be as bad as I think.
Remove the airbox, put on some pods and use the copious space that frees up; This is a pretty common mod for bikes, though I must admit I haven’t seen it done with many Maxims. The biggest drawback I see immediately is that the side covers attach at least partly to the airbox, so I’ll have to come up with some kind of bracket to replace that function. A lesser issue, but one worth attending to, is that the throttle bodies would lose the support that the airbox affords. The throttle bodies have a bracket that was pretty obviously used to mount them to some sort of support on the original bike. I should be able to utilize this.
As for the carburetor to throttle body swap, the carbs appear to be 67mm apart for 1&2 and 3&4, but 80mm for 2&3. I was guessing about 10mm just eyeballing it. If I elect to lose the airbox, it might make it slightly easier to add a spacer between the two banks and kind of ignore the 3mm difference between the fixed TBs.
I could not get my calipers between the boot and the body of the carb to get an accurate measurement but I would guess that the OD of the carb throat to be 32-38mm, whereas my TB is 57mm. Ouch. I have my eBay eyes on other TBs, just in case.