I would definitely cross-check the transmission number to make sure it will fit.

I did a swap in a 123, and it was no big deal. You need to have the new flywheel statically balanced to the old one.

I was contemplating a swap for my 250C. Here is the email exchange that I had with a parts source:

From: Michael Medill [info@mercedesusedparts.com]
Sent: 11 October 2000 07:02
To: Chuck Taylor
Subject: Re: Parts Request (Long)

hello, i can furnish you with everything you need, right down to every nut
and bolt, with all the new parts you want, for $1300. this would be for a
4 spd.

At 12:45 PM 10/10/00 +0100, you wrote:
>Gentlemen:
>I am restoring a 1972 250C (2 door coupe) in Falls Church VA. It is
>currently completely disassembled.
>The Chassis Number is 114.023, and the Engine Number is M130.923. The
>complete VIN is 11402312000724.
>
>All 250C's sold in the US came with 4 speed automatic tranmsissions. While
>the car is apart, I would like to at least explore conversion to a four, or
>ideally, a five speed transmission. I am wondering if a 250CE would be a
>potential parts source.
>
>What I require is basically all of the parts to convert the car from
>automatic to manual. Here is what I can think of:
>
>Flywheel
>Clutch disk *
>Pressure plate *
>Throw-out bearing *
>Clutch actuator arm
>Clutch slave cylinder *
>Clutch master cylinder *
>Hydraulic fluid line from master to slave cylinder
>Clutch pedal assembly
>Bracket to hold clutch pedal
>Brake pedal pad
>Transmission
>Shift linkage, including backup light switch
>Shift handle, knob, boot
>Driveshaft (if different from automatic's)
>
>* Indicates a new or rebuilt part would be preferred

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe