1998 740i - Need help determining value

Hello - I have taken custody of a 1998 Dark Green Metallic 740i (sorry don't know exact color name). I am about to sell the car for my mother-in-law who is moving to the city and no longer needs her ride. This is not your everyday E38 and would love feedback from enthusiasts and realists alike about its value (or lack thereof).

Odometer reads somewhere around 55k miles (not a typo). HOWEVER, my mother-in-law's evil stepdaughter took the car out one night and blew the motor. I've abused my fair share of cars, and it took some serious dedication on her part. Anyway, her ex-husband took the cheap way out and brought the car to a shady mechanic who pulled the blown motor out and replaced with a slightly older 8cyl from a 5 series (he claimed the proper motor couldn't be found - I think LIAR!!). So we have a 90-something 5 series motor with a '98 7-series computer - which is a very bad marriage. Issue that is most prominent is VANOS sensors do not line up or communicate well, so the car has trouble starting. Takes 3x (give or take) of starting it (then it dies) until the sensors are close enough that it stays running and you're off. Once you're going all is fine, minor issues of air/fuel ratios etc, but I've driven it from S FL to Tampa and around town for the last year with no issues. I've spent a few hundred dollars at local bimmer mechanic to see if he could put a spacer on the VANOS or figure something out - but no luck. He says the motor is good/strong, and the car itself is in great shape. Mechanic said I could/should sell the 5-series motor, use that cash to buy proper 7-series motor and have it installed and car would run for another 10 years. Problem is I don't have that kind of cash on hand at the moment, nor the cash to buy the car from mother-in-law to begin with.

So, if I am about to list this car for sale - how do I price it? It's running, interior is in great shape for 12 year old car, no tears in leather, carpets are clean. Radio display is illegible, but radio works, has CD changer in trunk - also working fine, sounds like some speakers are blown (easy fix), only other issue is seat cables need to be adjusted, headliner is starting to sag, and right rear window needs new regulator. AC is great. Mechanically most components are barely broken in (judging by some of the mileage I've seen on cars in these forums). Exterior is in good shape too, some door dings, some flaking clear coat on sideview mirrors and behind sunroof - but all in all still a very attractive looking car. Wheels are in good shape, no body rust that I am aware of. No accidents. Car had been garaged until it came to my house, been parked on driveway for a year or so.

One more twist - in return for all my hard work (and because I am such a wonderful person - my words of course)she has given me a '92 525i w/ 95k miles. It needs quite a bit of TLC to bring it back to all its glory, but mechanically it is not the Frankenstein that the e38 is. My plan was to keep this car and bring it back to life. Is the e34 worth selling and splitting proceeds to fix e38? Or is the e38 bound to give me a life of pain??

Any feedback/help is greatly appreciated! Haven't taken pics just yet, hope to get them posted in the next day or so.