BMW Repair: Blown Engine?, bmw shop, planning a road trip

Question
I have a '97 740IL with 73K miles, last 10 of VIN are 26VDMO3503. We were planning a road trip and had car checked for necessary repairs, oil change, etc.  Needed new water pump and hoses so had them repaired (non BMW shop.) After 10 days on the road, radiator overheated, no indication from gauges, engine began sounding rough and check engine light came on, pulled over and shut engine down.  We were traveling and had it towed home then back to the same shop who diagnosed it do be a blown engine with no reading on compression tests, etc. and of course in need of a new radiator.  We had it towed back to our home and here it sits.  It will start and run but sounds rough.  Can you advise of what you think and if you think it is worth taking to a BMW shop to be further tested and possibly repaired or if you think it in fact needs a new (or used) engine replacement.  Thanking you in advance.  

Answer
What was the code when the check engine light came on?Taking it to a BMW shop will probably get you BMW prices.Find out what the code was that caused the light to come on .It may have to do with overheating but would like to know to say for sure. No compression?What was it? You said it ran but sounds rough.It would be nice to know if it was 1 or 2 cylinders or how many read zero if they do.It maybe just headgaskets being that it overheated and they are aluminum heads,so it doesn't take much to warp the head.
I would do a compression test on all the cylinders and see which if any are bad.Check the codes to see why the light came on.73 k on a BMW is just break in period I think,they last for a very long time.Actually most I work on they buy them with 70k and some now are pushing 200k.
Used engines are probably out there but pricey for sure.But having only 73k on it I would look more into the motor as it sits ,checking it out first.Look for a good tech they are out there.