Have I blown it up?

[BogfordGarage]

Hi I have been on this forum for sometime but have struggled to find time help others, hoping someone can help me with this one.
I have a 1991 940 TD, with a few minor mods i have added in my 2 year ownership.
This weekend she threw in the towel after I accelerated at speed in reverse gear downhill and i think it overran (operator error I'll admit). It maybe difficult to visualise but essentially I revved hard and as I let off something went pop and it then made a noise resembling a rev limiter on a petrol engine throwing out blue smoke and then stalled as i came to a stop.
The car starts but dies out quickly unless you apply the throttle, when throttling the engine just surges in firing order and stalls out if you let off, it also white/blue smokes, no rattles or metal noises can be heard but the temperature climbs quickly.
My dad who has had a lifetime working on petrol engines suspects the head gasket, myself thinking its more like piston rings.
Some background; Timing belt 10,000 miles ago, valve shims checked and changed 2 weeks ago, fuel pump belt and pump timing done last weekend, due and oil change but not desperate, fuel filter 2,000 miles ago, Turbo rebuilt (by professional) 20,000 miles ago.
Modifications (all added 20,000 miles ago); Large intercooler added, Fuel pump boost compensator and fuel air mixture adjusted for more power, boost pressure regulator added to run 1 bar (15psi) peak, oil catch can added, straight piped to side exit.

Hope this is enough info and help would be appreciated.
Many thanks