Thanks, I wasn't aware of the rule of thumb. Actually I didn't expect going to a larger chain ring would be a complicated affair whatsoever.
I think you're making it a little bigger than it really is.
Follow the basic rule for sizing the chain.. There's plenty of youtubes and again there's a little leeway and not critical down to an exact link count. If unsure go a little longer as it's much easier to remove a link then it is to add.
The Ultra mtb spider doesn't have enough offset to mount an inside guard.
But if you're not having a problem then there is no need.
And though the guards main purpose is to protect clothing... yes they can aide with chain drops.
Did a bunch of work on my bike today... New wheels, tubes, tires, chain, tensioner and yes a chainring. The test 46t went right on and I reinstalled the 40t guard so the bolts didn't protrude the nut on the backside leaving the threads exposed to damage. My luck I'd bash one on a rock making it a bitch to remove.
Fyi.. The spider, chainring and guard are all about 4mm each in thickness with the spider sandwich'd in the middle.
Went for a 25mi ride afterwards and I like it. Moved me a gear down making my lower gears more usable and my highest gear almost impossible to spin out... all still feeing easy to pedal without extra motor input. I'm curious to see if my average wh/mi changes.
I just ordered a proper guard... Now it's your turn, get to work!