Yes they are interchangeable. The 580 is a single shot bolt action and the 581 is a clip fed bolt action.
According to Remington 60,000 from 1967-1987.
Push the safety lever fully forward to dis-engage the bolt stop. Then the bolt can be removed rearward.
No
$ 375
Model Five Model 33 Model 34 Model 341 Model 37 Model 41 Model 411 Model 504 Model 510 Model 511 Model 512 Model 513 Model 514 Model 521 Model 540X Model 541 Model 580 Model 581 Model 581S Model 582 Model 591 Model 592 Nylon 10 Nylon 11 Nylon 12
They were made from 1967-1987 and are date code stamped. See related links for details how to look up the manufactured date.
$60.00 Current prices on various firearms board seem to indicate the prices for Remington 580s are on the rise. If looking for one, expect to pay $150+ for a nice, servicable rifle, depending on condition and locale. Rimfire benchrest shooters in my area (NW AL) are buying up 580s and rebuilding them for benchrest competition.
A Case 580 backhoe loader weighs around 15,000 to 17,000 pounds, depending on the specific model and configuration.
Impossible to answer without knowing who made it.
580 + 580 = 1160
35% of 580= 35% * 580= 0.35 * 580= 203