The timing cover should have a number with a circle of dots around it also. This is the date code and will help tell what year the cover is anyway. The number ex: 68 inside the dots is the year cast. The dots around it will determine the month. Now there should be a C8 casting number on the side of the block if it's a 68 engine. C8AE-A. C8AE-C and C8AE-E are a couple of 68 390 block casting numbers. It could also be a C6 or a D3 number as well. Down by the oil filter adapter the should be a number/letter/number(s) code on the block. This is the date code for the block so try to find it also. It's on the block underneath the oil filter adapter pad. Also between the center two spark plugs on the heads you will see a casting number like the block. If it's a 68 head it shold have a C8 number like the block. The head date code is underneath the valve cover above where the casting number is and will be a number/letter/number(s) like the block. The crank and rods and almost everything on the engine will have a casting number and or date code to ID it. You can also take the head off and measure the bore of the block. A stock 390 has a 4.05 cyl bore but keep overbore in mind. So take a look and see what you can find. G.