I know this has come up before about these conversions but A)how do I mount the clutch pedal? B)the car is a 142E do I have to change the rear end? C)do I need a front drive shaft?

The clutch pedal mounts differently than a 164. The best way is to get pedals and all the mounting for both. The clutch mounting can be cut from the donor car and welded or bolted to the other car, I did one that way and it's still on the road.

Your rear end is fine, you don't need to change it.

You will need a different length driveline except possibly with some early 140's that have a longer BW35.
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Lee 75 244 (80k original miles) 79 242 65 220 project

Here is what I understand on the auto-to-manual conversion from my research on converting a 164:
A)At least on the early cars, the hole to mount the clutch pedal is pre-drilled in the pedal box. However, the auto cars are missing a reinforcing plate at this hole. Changing out the entire pedal box is the desired approach as the weight of the clutch will stretch the hole in non-reinforced box. This involves removing shear bolts and pulling out a section of the wiring harness to change the box.
B)Changing the rear end is recommended for the swap. If this is a 1971 142E, it probably has the 4.1:1 rear axle. Manual 142E's had a 4.3:1 rear end and M41/B20B equiped 140s had a 4.56:1 axle. If the auto axle is kept, overall ratio in top/OD will be 3.26:1 compared with 3.42:1 and 3.63:1 respectively for the E and M41 axles. I would opt for the one of the numerically higher ratio axles (4.3 or 4.56:1) as the auto one might be too low of a ratio for the engine at cruising speeds. Remember, 3500-3700 rpms for sustained periods is no sweat for the B20s.
C)Yes, you will need to change the driveshaft in some manner mount the M41. Either a front driveshaft section is needed or the driveshaft can be professionally shorted and balanced. The first approach is totally reversible, but the latter is a permanent change.
Check out this site:
http://www.buvic.com/car/repairs/transmissionswap.html
That was little more long-winded than I hoped for... I hope I answered your questions.
Nick

I must disagree completely about the rear axle. Consider yourself lucky if you have a 4.10, as that's the one you want. Many years ago I converted a 72 145E and the 4.10/M41 combination is close to ideal---clearly preferable to a 4.30 with the same transmission (I had a 71 142E that came stock with those gears, so I am familiar with both) The gas mileage is better with the 4.10, highway cruising is quieter, and acceleration does not seem to suffer much, if any. My wagon would happily idle in second gear, on level ground, at a speed of about 7-8 MPH.

If you will be using a straight 4 speed (M40) you will be OK with a 4.10 (that's the way most of them came from the factory) but a taller gear from a 164 (3.73 or even 3.54) would be a better choice. 4.30 with no overdrive is tiring to the ears on the highway, and 4.56 would be absolutely miserable. While 4000+ RPM all day long won't hurt the B20 in the short to medium term, it will eventually show up in the form of added wear, and it will definitely waste a lot of gas getting there. Try to obtain gears that will give you 2500-3000 RPM at you preferred cruising speed. (4.10/M41, for example) If your engine is healthy, it will pull these gears with no trouble at all, even in a wagon with a full load. The fuel injected B20, whether E or F, is very flexible, with no shortage of low end grunt.

I would like to qualify my suggestion of a lower geared axle, and perhaps learn something in the process. I was under the impression that a final drive ratio was chosen to allow the engine to achieve peak revs in top gear and cruise comfortably at or close to peak torque. I won't argue the fact that a lower ratio rear will reduce engine noise, speed, and wear if the engine is healthy enough to pull the lower ratio, but at what point is the ratio too low? Comparing apple with oranges again, I have heard that using the auto diff(3.31:1) on a manual swap in the 164 is too low a ratio for a stock engine in overdrive. Assuming an M41 is used, wouldn't a 140 have the same problem with an auto diff?
Help me out; Is my thought process off?
Now a little confused,
Nick

thanks you certainly helped