Last things first:
you'd need to drive a million miles to turn over the speedometer- they have 6 digits so they count to 999,999. Not too many make it that far but 200K, 300K, even 400K is not unheard of on original engines. On the otehr hand, the speedometers break much more frequently than the engines... so it could well have been broken for years. I wouldn't worry a lot about the mileage, especially if the engine passes a compression test.

You can use the B23FT in your car, but for a 740 you'll need to make some changes. You'll need to install the 740 distributor to the back of the head, and get the block-off cap for the hole in the block where the 240 dist was. You'll want to check the turbo arrangement to see if you've got a watercooled one. It isn't worth installing one that's only oil-cooled. You may need to make changes to the turbo oil return line to accomodate this change. It's a real good idea to replace all the copper washers on all the turbo oil lines anyway while the engine is out- tough when it's in.

What's wrong with your engine anyway? Lots of piston slap or was it overheated? Symptoms?
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Rob Bareiss, New London CT ::: 86 244DL, 87 244DL, 88 744GLE, 91 244: 808K total