Okay, forgive me for being a newbie, but I want to make sure I didn't get screwed on the car I bought. I am trying to decode the engine. Casting numbers are 3789817. The last 8 almost looks like a three but it isn't. I don't know if that is common. The engine number on the front are T0427D? When I look up the suffix it tells me it is a 283 powerglide from 1958-60? He told me it was a 65 327. My car is a 65 chevelle that was once a 6 cyl and is now converted. Please help.

That casting number was used for both 283 and 327
check here at Mortec.
http://www.mortec.com/castnum.htm

The single digit D code for 283 was used 58-64 for Impala. Not just 58-60. A '65 327 should be a two digit code.
The casting date will tell the year of engine. Look for the casting date code on top rear of engine.(may be on either left or right.)Will be a small raised letter for month and numbers for day and last digit of year. (D254 for ex is April 25th '64)

So I most likely have a 64 283, not a 327?

I found references that show the 3789817 as '62-'67 327 2 bolt main only. No reference to a 283. There is also a 'tell' on the front, pass side, top of the block, near the water pump. There is a 'fin' that sticks out and someone that's familiar with the differences can see which it is by the placement of the fin.

Hey Shooter. Where did you see the info showing 58-64?

I'm not shooter but he used Mortec as shown above. Normally a solid reference. I usually use it also. I also use http://www.nastyz28.com/decode.html Has mostly good data and a broad range of info. I do know that a late 283 can handle a 4" bore so it is possible.....