Can the pipe and cylinder head from a 72 DT2MX be installed on a 69 DT1B to improve performance?  Not making the DT1B a racer, just want some performance improvement with these parts.  Also, can the RT1 32mm Mikuni work on the DT1(with flange hole modification) or should I find a rubber manifold for a later 30-32mm Mikuni?  I may use the DT2MX car if I go that route.  Thanks

I believe the dt2mx head will fit, but your compression might be way too high and require high octane race fuel.  The port timing is quite different between the 2 cylinders.  The dt2mx gyt pipe WILL NOT fit under the gas tank.  Many years ago I put an rt1b carb on a dt3, and it worked well for not messing with the jetting.
if it were me I'd focus on raising your compression to a static of like 7.2 or 7.5 to 1 by shaving the stock head, or having someone weld it in and machine a new chamber.  I think the dt2mx head will put you over 8 to 1 compression, with the stock dt1 cylinder.

I don't know what length rod the DT2 MX  uses , but the DT2 and DT1 have different length rods .
It's probably not just a bolt on , top end job .
 

If ya only talking the 'head' not complete top end, i tried a DT1GYT kit head on my std dt1 but extra pressure just made the piston rattle more than usual.
So compression ratio would have been similar to what your talking using a DT2MX head.
Nice looking head that with tall fins.
Which also has me thinking it won't be cut away for the original exhaust to sit close.
As has been said the cross over pipe won't fit through the frame.
Now there's another thought--in the early days there was a DT1lowering kit where you cut the frame & add bits which would then probably give room to pass the DT2MX pipe through the frame. So then you might as well go the whole way & fit the 'go fast' cylinder except you need a rod length change. Cant remember if DT1 is too long or too short. Think too long so a 5 or 6mm base plate would fix that if i'm right.
Loved my New DT2MX.
Found a pic of it lol. Reminiscing from when i was young haha.
Here's my DT1 with GYT kit & altered swinging arm, can see my welds.
Arm used to break near the front right side, amazing the stresses that happen in racing & where they show up. Lucky i spotted that break while heading off to a race meet.
photos.app.goo.gl/MwdUdpcD7hfGJBjE8
Second pic is my DT2MX just a great bike. First production MXer from Yamaha.
photos.app.goo.gl/bTqS5m259iWMzaUu5
Sorry, just a bit of Bull #$t couldn't stop myself haha.

Morley awesome pictures. 

Haha 50+ years ago when i was only--ahh--about 24.
Bring back the "60's & "70's.

Thanks for all the information and old pics. Looks like there's nothing really helpful from the DT2MX for my 69 DT1B. The DT1 engine is only .25 OS piston and otherwise fairly stock. I'll look for a local machine shop to flycut .010" from the stock head. Planned to always use premium gas, race gas is too much. Probably go to Sudco or K&L for the carb holder to install a 32 Mikuni.

Best off to use the newer clamp style flange with rubber boot, vs 2 bolt flange.  But I have some rt2/rt3 vm32 carbs if interested.  They have a tendency to get warped a tad and not seal perfect.

You are the real deal Morley!  I love the vintage photos.

It’s sad that the actual hold in your hand pictures will no longer be a thing for young ones like my grandkids. What are the odds that they will ever be able to share 50 year old photos like Morley just shared with us? I realize that it’s feasible. But highly unlikely.

Rt325, I don't think you can b.s. too much around here.. lol.  Who else wants to invent a time machine?