My thoughts on this have recently changed!!! I just upgraded what was a perfectly goog TD for a tdi. The TD had covered 8000 miles with me with not a hiccup, and 100+ before that (but can't vouch for that!) and although it was a bit sticky to start from cold and tended to suddenly rev away, then stall but generally was reliable. I was getting 22 miles per gallon, foot flat to the floor all the time (living somewhere very hilly), driving round quite a lot in second, third on motorway hills, Trewey flying past me on anything more than a 1:100 incline.
Got a bit fed up (as it is now my daily driver and i do a reasonable mileage) so i got a 200tdi put in. Now i realise what an old dog the 19 was. Am getting 30+mpg, it goes when i put my foot down, 5th on any motorway (or cornish equivalent), 4th on hills i used to struggle on third in, and yes, it came with a free chuftee badge
And yes, they do have a bit of a reputation for not coping well with the turdo (! cos it sure as fook ain't a turbo - maybe they just stuck a Turbot on the side - SIRUS???) although i never experienced any of the unreliability issues with mine. The TDi starts before the engine has done a full revolution whereas before it was try a bit, heat her up, try a bit more, heat her up and eventually if the battery still had enough juice, she'd fire.
So all in all the 19J is bog standard, the later ones were better modified to cope with torbocharging but i'd say it was a serious compromise, and i did a fred a coupla weeks ago where i worked out that the TDi conversion would pay for itself in well under a year id doing reasonable mileage.