Gene, what is the distance, from the front of the first throttle to the back of the last one?

I  dont know if thats a -64 thing but i have seen several 64 blocks that way

The old streetmaster looks to work quite well!

I use an ATI c6 flex plate and a powermaster starter 0 problems at all. I been running mine for about a year now and I had the inspection plate off not that long ago and teeth looked good.

I will say that when I had my converter made it was made with 3/8th bolts and the ATI flex plate was 7/16 not sure why the converter guy did that just lazy I think but I fixed that with out any real problem.

something else to add did you buy the kit? flexplate and crank adapter kit? or just the flexplate?

There is about a 99.9% chance that it doesn't have 427 cylinder cores but, it could have a little thicker cores in it.

Are there any markings on the rear of the block? A picture of that area would help, a lot. Of course a sonic test will tell you what you have to work with. Also, you can pull the expansion plugs and measure between the cylinder walls with drill bits or, I use Allen wrenches and get a good idea of the thickness of the walls by how much space there is between them.