Check every inch of the frame tubing - they are notorious for cracking, just like the formula cars they were based upon. Gas welding is OK- it's just mild steel. I was at the Misano track in Italy when the Swedish Pantera Klub rented the place and one owner with his Vallelunga was also there. The little car had NO problem keeping up with street Panteras on the track and the Swiss owner was around 6 ft tall.
If you get lucky and find one, a Lotus 1600 twin-cam aluminum head with Webers will bolt onto the block for around 200 bhp. In a 1400 lb car (with driver) that should be sufficiently exciting. Tom Matano, designer of the Mazda Miata owns/owned a Valle' and said it was his inspiration for the Miata concept.