1200 would be my limit. on the back i have 4.11 gears on a 9" rear end. I had heard that it was alot more complicated going from a 3 speed automatic to a 5 speed manual than 3 to 4, but if it isn't id go with the 5 speed in a heartbeat.
1. for that $$$ I would recc E-boks or Roush 200s (Darts, Windsor Srs, whatever they are calling them these days).
2. I converted from a C-4 to T-5. Not any more trouble, esp with a cable clutch setup. The overdrive would REALLY help that 4.11 problem you have there :: Several other folks here have done this as well.