Very few Series I z's were made in January 71. The actual month of manufacture is posted on a placard in the driver's door jamb. Mine was made in the last week of December 1970 but wasn't titled til June 1971. January 71 cars were sometimes a mix of Series I and Series II parts as Datsun used up their inventory. I believe the last Series I car was around SN 21000.
Series I heads were type E31 question is whether just the head was changed or whether someone swapped out the engine with an L28. The placard in the engine bay has the vin and engine serial number on it. A numbers matching car will be worth more to a restorer.
CLASSIC MOTORSPORTS magazine recently had an article about 19 classic cars that you can afford to buy now for future appreciation. The Series I Z was first on their list. They recommended preserving the car for the next 5 years and letting the next owner doing the full restoration. Basically they were saying make it drivable, don't hack it up into a racecar, but not to worry about the plating on each and every nut and bolt.
Most parts are available today but some are becoming rare and may be hard to get in five years. Rust free California cars are valuable to the rest of the country. Places to look for rust are under the battery tray, the sub-frame rails supporting the engine and front suspension, under the front fenders near the windshield, the dogleg areas in the doorwells, and the bottom of the front fenders.
While the NICO members are a great bunch of guys, there are other early Z sites that focus on these cars. A great site is
http://www.classiczcars.com/
Keep us informed on your progress, vin and date of manufacture.