Here is another way. I used this on a 124 with M104 motor which is supposed to have the harmonic balancer bolt torqued to 400 N-m (yikes).

Place car on jack stands, then get under the car and remove the plastic inspection cover plate on the front side of the bell housing. Yours might be missing - mine was. Rotate crankshaft until you see the M8 bolts that attach the 'spider' carrier to the flywheel (flywheel to torque converter) visible in the opening. Remove one of the bolts and in its place screw in the following tool:

Get an M8x60 hex bolt, at least grade 8.8 but preferably 10.9 or better. Fabricate up a thick tube/bushing to go around the OD of the bolt using a 3/8” NPT schedule 40 pipe nipple, 3” long. Cut off the two threaded ends of the nipple so that the overall length of the nipple is 1-1/2” long. Then, into the ID of the nipple, drive in a 21/32” OD x 3/8” ID steel spacer bushing into the pipe nipple. The bushing just fits exactly in the nipple ID. The pipe nipple and bushing both came from the hardware store. Place two 3/8" or 5/16" hardened SAE washers under the 8.8 bolt head and then slip on the bushing. Mark the 60mm bolt so that you have a net 50mm bolt length available under the washers and then cut the bolt to this length. Dress the cut-off thread on the bolt so it screws in easily, i.e., file off the burr. Now screw in this assembly into the hole in the torque converter that you took the other M8 bolt out of. Now rotate the crankshaft until this bolt and bushing catches on the bellhousing. This will lock the crank. Now use a pipe snipe with your ¾” drive breaker bar to bust the harmonic balancer bolt loose. It takes a lot of mustard to bust that bolt loose.

This is a good method because it doesn't require you to have a helper to hold a screwdriver in place under there while you rotate the crank. You can screw in this tool and work solos at your leisure and you don't have to worry about flying tools. This job is not something to muss around with.

Don't try to do this without the bushing on the bolt because the bolt is not stiff enough. You will just bend it when you apply all that mustard to the breaker bar. Pete