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Net hp numbers instead of sae numbers, dropping from 11 to mid 8 compression ratios weak cams due to emissions standards and open chamber heads with smaller valves dropped the performance tremendously.402, was the same engine as a 396. In 1970, GM did some changes to the 396, and it became a 402. For 1970, GM still called it a 396 though. The 396 was so we'll know by the public, GM didn't want to loose that rep, so they keep calling a 402, a 396. A 402 can be built to make some good HP. They were around 365 HP stock, I think. No to hard to build that into the 450-500 HP range. A number matching 402 SS Chevelle would be worth more money than one with a swapped engine.
If the TH400 that came with it was numbers matching I would have kept it auto, but it came back as being from a 1982 Chevy truck.Net hp numbers instead of sae numbers, dropping from 11 to mid 8 compression ratios weak cams due to emissions standards and open chamber heads with smaller valves dropped the performance tremendously.
Just my opinion that you didn't ask for, I don't consider a mid 200s engine a performance engine. Yes, if you cam and head swap then you'll get a decent runner but if your going to go big block, go big. Justin's comment about a manual swap made me think that he wanted to enjoy the power of a big block.
Otherwise restore it back to stock (including keeping it an automatic) and enjoy its value and drive it like anything can happen to it at anytime.