I have been using the coin type gauges for spark plugs for over 50 years and found them to be close enough. Champion used to give them away. I think wire are actually more accurate. A Blackhawk MT-1021 has the round gauges required for HEI. They are made in USA and cost around $10 For valves, I use BGS Werkgeug 12 blade gauges with a bent end. They are almost a must for Y-Blocks and handy for GMC. They are made in Germany and can be bought for about $10.
