I have one in my 84.  I've run about 35k miles since I got it as a done deal
without any lifter problems.  Mine is the 1.8liter from a '92 Cabriolet with
digi II injection.
  If your mechanic just did the conversion, perhaps he made some errors in
the initial valve clearance setup..I don't know, having not yet put in
another 1-4 (hopefully, I'll go another few hundred thousand miles till I
need that) but I understand you must 'pre-adjust' the lifters somehow until
they "inflate" themselves to the proper clearance..Maybe he would em in
there too tight, or something.
  I had one lifter that was a little noisy after a long period of not
running, but I recently put in a more aggressive camshaft grind and since
then, I have not heard the "ticking" I used to get for a few seconds on cold
start.
  I'd have him go back inside the head and check it again...It's super easy
to take off the cam and get into the lifters..maybe he got one mounted
crooked or something, or got a speck of grit in there...I don't think you'll
find it's a 'system problem' with using the motor tilted over...Many people
do it without problems..I really recommend that conversion for anyone
looking for an economical simple inexpensive and dependable alternative to
the WBX motor..
  Don Hanson