ARP do stretch. They have guidlines as to what is acceptable and what is "out of spec"....to 9 out of 10 weekend warriors its not much to worry about. Guys who rebuild often know enough to check them on each rebuild.....never trust a part to be "in-spec" even brand new out of the box....
have you got the block torn down yet?
Just adding to your post.
Yes they do stretch. Like previously mentioned all fasteners stretch when properly torqued as that's the only way they stay fastened.
Something people don't think about is rod bolts. ARP8740 have to be checked and usually shouldn't be used more than once unless you have the original measurements to check against. ARP2000 are generally good for reuse.
There is plenty of information out there. Search terms like yield, plastic state, tty.
TTY fasteners stretch into the plastic state. The plastic state happens after the elastic state is exceeded. Once a fastener is in the plastic state it doesn't recover and can't be reused. A properly engineered tty fastener enters the plastic state at the same clamping force as needed for the application. This ensures proper torque and prevents over torque. Over torque can lead to metal fatigue, warping, and metal displacement.
I'll preface this with my own experience. I've been using calibrated torque tools for over the last 24 years. Torque values are important enough in my job that I have to record the sn and expiration date of the certified tool, fastener types, and torque value used. One thing that you should never do is double torque or "check" already torqued fasteners. In most cases it adds excessive torque.
Anyone can check any of this information out for themselves. Just spend a little time searching. Ford has some pretty good reasons for building motors like they do. Just because it's not what was done 30 years ago when hot rodding a 350 doesn't mean it's wrong. Search, learn, don't take anything anyone says for granted.
Good luck with the rebuild.
