Pipe plugs: Take the sender to the store and match the threads...or measure and compare to web chart.
Gauges: They come off the cluster easily. No special tools or drill out. Buy a gauge, buy the tubing and plumb.
You can buy new "faces" for your gauges.
Gauge work is much easier from the front instead of crawling if you can remove ash trays, radios, speaker panels, delete plates, glove box, etc. on some trucks, Check that out.
DADS50 has a lot of advice on all this.
