You know I have an easy way to check the block to give you a better idea of what it is. You may have used it or heard of it before. The drill bit test....this is where drill bits are used to gap the space between the cyl walls The freeze plugs need to knocked out though. You gap the cyl wall with the shank of drill bits in 1/64" increments. As follows for a 352,360,390,410 block a 17/64" bit is used and for a 428/406 block a 13/64. As I said use the shank of the bit to size the gap between the cyl walls. This is a basic test that will give you a very good idea what block your dealing with. You will find some rust and maybe casting sand and the gap may be plugged with crap. Clear it with a butter knife or something first. Check gap at top middle and bottom. The fit should be snug not loose. This test has been laid out using 1/64 measurements for ease of understanding among the masses. You can substitute different bits in 1/8th measurements or whatever as long as you convert the measurement to 64ths to ID them. Hope this helps it's a good guide and sorry I did not mention it sooner. G.