A Cleaner Approach

from collections import defaultdict

def identity(x):
  return x

transformers = defaultdict(lambda: identity)
transformers.update({
  'Id': int,
  'Type': int,
})

for row in reader:
  transformed_row = [transformers[key](value) for key, value in row.iteritems()]
  json.dump(transformed_row, jsonfile, sort_keys=True, indent=4, separators=(',', ':'))
  jsonfile.write(',')
  jsonfile.write('\n')