Yes, there was a conversion made by a guy. I'll see if I can find the picture of it. Only one was made, as I recall to see the feasibility to certify a conversion. For some reason, that never came to fruition. Part of the problem, as I recall, was that with the lesser weight of the turbines, the engines would need to be moved forward, which would preclude the normal clamshell entry. I think the prototype had a ballast in the back to compensate, which was not an ideal solution. BTW, this was also the case with Speedster 850 which I saw in person in builder Oscar Taylor's hangar (he's building a new shortened one based on an Aerostar but with a Garrett -14's in it, which should be an absolute rocket).
Aerostar is a great performer and with a pair of turboprops, it would be stellar. I have never flown a better handling airplane than the Aerostar - they're in a league of their own. The jet conversion they're planning is interesting. Not going to be cheap to do it, and it will perform well, but with the prices of used Mustangs these days, don't really see a huge market for it.