[Jack21]

In the U.S., the '68 - '74 blocks are alleged to be slightly beefier than the '75 and newer. For bottom end strength, It's more critical to use the correct fasteners to keep it buttoned up.

My 351W block is a '79, but all the critical hardware is ARP, with studs, rather than bolts on the main caps. A 393 stroker mostly street is not going to break the bottom end.

In the U.S., the main reason earlier blocks are used is for emission control requirements based on the year the car is registered as. In many States, the year that the car is registered as is based on the year of manufacture of the engine (based on the ID of the block). "Engines", in cars over 25 years old are generally emissions exempt. Other registration options such as Classic, or Antique is available. Some guys will buy an old Galaxie, the entire rusty old car, just for the right year engine in it. Yank the motor, and junk the rest of the car, just for a (more-or-less) hassle free registration process at DMV. There is no hassle free titling process at DMV for a freshly completed Cobra, each State has different requirements, so the builder must know exactly what the requirements for parts AND documentation are before spending a dime on kit, or parts. Ask me how I know. And it may not be any easier for you Aussies, Brits, or Canadians.

So, in the U.S., if an '87 engine (block) is used, and there is no circumventing rule in your particular State that allows "Specially Constructed Vehicles", or year of the vehicle registration to be the year of it's original replicated manufacture instead of the year of the engine currently installed in it to be used. Then be prepared to install catalytic converters in your sidepipes, and pass HC, and NoX (and a variety of other oddball issues) requirements for the '87 (or whatever year) car you took the motor out of.