I just recently scored me a 1971 Yamaha RT1M! unfortunately the pipe is a supertrapp instead of the stock one and someone cut a few cylinder fins to fit it. Im curious to know a little more about the early MX bikes, specifically years 68-71. Ive noticed that when im pulling up parts diagrams its listed as an RT1M instead of RT1MX. My theory is that Yamaha had a GYT kit in 68 (maybe sooner) and they just tossed these on the enduro models and stripped all the unnecessary stuff off making it an M. However when 1972 rolled around they started making an actual MX bike with its own unique pipe and other features but the GYT kits were still available to make these classics scream even more. This is my theory anyways, hoping to learn more about the race models and kits.

Not quite the case . The RT1 M was the dedicated motocross bike for 1970 ( first year available ) .
In 1971 it was relabeled RT1 MX . I cant comment on any differences between the two ,
though I'd suspect they were relatively minor .

Lucky you!!. I'd love one of those. Assembled my bosses one new. Looked great in black. Might've been "71 not sure now but i'm sure it was the RT1MX not just M.

Not to rub things in further but i also scored the "holly grail" 68 DT1 . Yes you are correct swoop i was up way too late looking at this thing. The stock pipe for this 71 RT1mx i think is a GYT pipe? 

Yamaha GYT (Genuine Yamaha Tuning) kits is not an "Enduro" thing.  They were available for the 1960's models...  I always wanted one for my YG1 engined 1964 MG1T. 

From what I've read, there were "GYT" kits for the early Enduros but if a "GYT" kit and a production "motocross" model both existed, the parts were not necessarily the same...  but they could be.   Chrome bore vs. cast iron bore cylinder was one of the differences between GYT and production MX parts in some cases.  There may have been differences in pipes and other parts as well.

I'm not sure if it also relates to the 360 , but the 70 DT1 M still used a chrome bore barrel , as in the GYT kit , 
though as Mark has said , they are not necessarily identical .
Whereas the 71 DT1 MX went to an iron liner in the barrel , allowing oversize rebores .
I'd expect the 360's of the same year were equiped similarly .

There is a 70/71 RT1M/RT1MX Yamaha manual in the Tech Library.  At the back of the manual they give descriptions and part numbers for the M/MX model parts...  It sounds like on the 360 the GYT and MX may have been the same?

After taking the time to check my parts manual , it looks like both 70 and 71 used a steel liner barrel , as
the pistons for both were the same , and available in std and two oversizes . There appears to be a typo in my book , as the
70 MX barrel is numbered the same as the enduro barrel , which I'm sure wouldn't have been correct .

An interesting read for sure. Ill have to read it again when im not so beat dead tired but it sounds like the GYT kits were made to be slapped on the enduros so they could become race bikes. I knew this could be done but i always thought the original intent was for these to be slapped on the MX models to hop them up even more than they already were.

I have a 73 LT MX100 that has a GYT pipe on it and she is a screamer to say the least! im not sure how long the GYT kits were available. I do know they were around in 68 and i assumed they made those kits until probably 76 but now that i think on it i dont recall ever seeing or hearing about any bikes newer than 73 having a GYT kit made for it.

Going back to my 360 im thinking that the stock pipe is an MX pipe that they designed for the bike and not a GYT despite it looking like a GYT pipe based off pictures. Mine has a supertrapp for the time being. Ill have to cross reference the part numbers for the GYT pipe and stock pipe in the morning to confirm what i just said.

As I remember it, GYT kits were made to hop up the standard models, not the competition (i.e. motocross) models. 

When the competition models came out, the GYT kits seemed to get phased out.  Which made sense because in almost all cases you could probably just use the competition parts on your Enduro...  and yes, by about 73 it stopped making sense because the competition bikes were quickly becoming more than a stripped down Enduro. 

LTMX came stock with a downpipe and it was screamer.