I am going to take the diffs to the LHS and see if the guy will let me take apart one of the diff cases of a 2005/2006 LSP; if these diffs fit in that case, then they would fit in the FLM bulkheads, correct?

if the pinion will mesh good with the diff and everything else fit fine you will be ok.
but i think they didnt invent the so called 7.5 diffs back then. i think that started later.

Looks like an old MP/Dominator diff (actually, it looks like the buggy the dominator and MP were based on!). Those diffs have a relatively large ring gear (similar to a savage) and won't fit a standard hybrid bulk. Funny - some of those diffs only had 2 screws holding them together as well - I think I have a couple of those diffs laying around the shop somewhere.

I will be getting the FLM hybrid bulks with 1/8 diffs in the near future when i upgrade to lipo. Mike was right about the diffs i had, they were too big. Is there a feigao 7xl without a built in heatsink, the only xl i could find on the website without a heat sink was the 8xl. I guess i will be keeping the original spur, what size pinions should i start out with? Pretty sure 15 is stock, how high could i go without damaging the 8xl? Don't want to do more than 40 or so right off the bat.

Stock on a E-Maxx is 18, but you will need 5mm bore pinions anyway, so I would get a Strobe slipper while your at it. Mike should be able to get you a 7XL without the heasink built in, but you will need to get a RC-Monster heatsink/clamp so the endbell doesn't pop off since there only pressed on.

what are the costs/benefits for getting a 8xl with/without a heatsink, do the ones with the built in heat sinks come apart like the ones without? Also, what is the highest pinion # anyone has gone on a 8xl?
Am i going to see a big difference between the 8xl and 7xl on 4S lipo that i couldn't otherwise make equal with a pinion change?

The cost would be about $30 difference. The 8XL with the heatsink built in will not come apart because the endbells are screwed, not pressed on. The speed differences won't be major, but you can gear the 8XL up to almost match the speed of the 7XL. If you plan on running 4S and 4S only, and not going up to 5S, I would probably go with a 7XL.

I thought the front endbell could still pop off the finned motors.

I don't believe so.

http://www.rc-monster.com/forum/showthread.php?t=5786
In the second post Sylvester said the front can pop off. I think some other people have said that in other threads as well, but I'm not sure if it's true or not:032: , I have a smooth can 7XL

Hmm....I suppose so. Never heard of that. I don't doubt it thought...

You can ask MetalMan or Cemetary gates.. it happened to both of them.

the finned motors are better than the smooth feigao motors, but they still can come apart. I had my 9xl pop the front end bell. I JB welded it back on an then it was fine.

What transmission upgrades do i need besides the hardened idler gear for the stock emaxx transmission with the 8xl/mm setup? The single speed conversions are out of stock and i just want to get it running for now. It is something that locks the trans into second gear, but i dont know what it is called or where to get it. Thanks for any help.

If you already have the steel idlers your set!