assuming you do the same amount of work as me is admitting that you generally do ****** all!!!!
Damn, found out at last.
Well, offering an opinion now, the aircraft shifted on the ground, and the trim (which I understand to be the cockpit surround, nothing to do with pitch control) indicates that something's moved in that area.
Combining the normally reading ASI and Altimeter, with the poorly reading DI and AI, along with the knowledge that pitot-static hose is generally less stiff than vacuum system hose, suggests to me that the stiffer vacuum system hose, rather than the (usually) more flexible pitot-static hose (or possibly it's connections) has become damaged during it's shifting causing a partial or eratic loss of vacuum.
The damage must presumably be between the off-take for the vacuum indicator and the actual gyro instruments, since if it was nearer the vacuum pump then it would show as a suction failure. My best guess is that it's probably at the nipples on the reverse of either the DI or AI.
You've mentioned by the way that the AI has never been brilliant - it could be that this was the final straw in a progressive failure?
The slip ball, in my opinion, is probably the most difficult - a vacuum failure when flying VMC should be nothing more than an irritation once it's identified. The fact that somebody who knows the aircraft identifies no handling oddities, combined with the ball being similarly out on the ground would seem to eliminate a bent airframe (which if it's undercarriage would only show on the ground, and if it's wing would only show in the air - and both being bent to show the same errors without distortion being visible or any handling problems seems outside the realms of reasonable possibility). There is no external input into the slip-ball which can be distrupted. The instrument panel in a C150 is wall-to-wall so enough distortion to move a normal slip-ball out that much would, in my opinion, be readily visible.
So, my best guess is that the slip-ball has become damaged somewhere out of sight. If the case, this is probably the only thing to endanger the aircraft for VFR flight - not because it's an essential instrument, but because a fluid leak into the cockpit can potentially cause incapacitation.
So, my suggestion, following on from Airbedane's, is to have an instrument fitter remove the instrument panel and check all of the instrument connections (note ALL, something else may have worked loose but not shown itself yet), along with serviceability and alignment of the slip ball.
But, I would also have an LAME do a rigging check to be on the safe side - forces large enough to shift a large concrete block via the tie-down point may potentially have bent something that you don't know about yet. To be frank, at the wing/strut tiedown point on a C150 I think that it's unlikely, but it does no harm to check whilst it's in the hangar.
G