going from 136 to 141, what mounting holes do i use? also can i use the stock skid? or should i use the m 141 rails? if i go with the 141 rails do i need the front arm out of a m skid? should i drill out the second hole up front? and also the second set of holes out back.

136 to 141 might not be a good idea.... Unless you are prepared to change your drivers. 136 crossfire is 2.52 pitch... and a 141 m7 track is a 3" pitch. Up to you though? And your really only gaining 3" or so of track on the ground. I'd suggest going to a 144" track or not doing it at all. If you go 144" I'd just 136-144 rail extensions and get a good 2"x15x144 track and call it good. I'm not quite positive but i believe u can stuff that under a CF without extending tunnel? Someone else can clarify on that though. Do a search on here its been done before.

already have 3pitch dirver on a new shaft.

In that case then just find someone that makes 136-141 rail extensions and go that route. You shouldn't have to move any of your skid bolt holes... Unless U are trying to do a rear skid set back? Before attempting this U might want to just bolt in your 136" suspension and see exactly how much slack you are looking at when your bogey adjustments are maxed out, Extrovert drives can run a ton of slack in the track. On my 153" M7 I run like 4" or so of track sag, measuring off the middle of the rails to where the track sags when u pick up rear end off ground.

If you do a skid set back... I'd suggest going back less than half of the extra amount of track you are adding... Example 141-136=5" 5"/2= 2.5" I'd suggest moving your skid bolt holes back like less than 2"... Maybe like 1.5" or so, your rear bogey adjustments can take up the slack of the rest. If you try getting it closer it becomes a rear pain in the @ss to get the bolt holes to line up.

Something else you are gonna want to know!!! You might need to cut a 3/4" or so off your front rail tips because of the Extroverts. I converted my F7 a few years back to a 151/153 and used 153x3"pitch track on it and had to trim some off the rail tips so they wouldn't rub on the extrovert drives cogs.

going from a 136 to 141 is not that much difference. go 153 thats what i did 08 rails floats 156x2.5 camo extreme. it should climb pretty good