I could be wrong but this is my guess regarding the vibration. The flywheel you have is for a 1970-80 383/400 ci. in. stroker engine that's externally balanced, providing your internal crank is from the 400 engine with spacer bearings to acheive your stroker combo which I don't think you have. The 400's rods are smaller in center to center distance @ 5.565" & pistons have a 4.125" bore therefore the crank is balanced accordingly.
Your stroker could have aftermarket rods 5.7" or 6.0" with 4.000" bore pistons x 3.75" stoke as well.
Most stroker aftermarket 2 pce. rear seal cranks are internally balance but they do make an externally balanced one.

Here's an option before you dig into the internals. Get a flywheel & balancer that's internally balanced and see if it ails your vibration issue. I realize its quite a bit of work and you have to decide whether you want a billet flywheel and good balancer or the inexpensive stuff to try? I say get the cheap 150.00 stuff first to try it out. Down the road when you decide to balance the reciprocating assembly splurge then.

Engine update
 

I ended up pulling my engine in late May. Most summer events were cancelled and I didn't have any good reason to wait until this winter.

I decided to go with a local machine shop/engine builder to have another 383 built from the ground up. The new engine will have a roller cam/lifters, forged crank, forged pistons and will be internally balanced.

The builder sent me a few photos. Hopefully, assembly will start later this week.

Daniel

Did you seek an answer to the original problem so you would @ least put it to bed? Just curious if the machine shop noticed anything odd.

ScotI- This new engine is using a different, seasoned, block.

I sold the old 383 to a guy who was going to balance it with his flexplate and put it in a K5 Blazer with an automatic.

The final consensus was the old engine's rotating assembly was balanced with a flexplate when built and my "off the shelf" flywheel was "off" balance enough to cause the vibration.

Daniel

Got-cha. Seems very possible.

I could tell right away on my very first drive with my new 383 that the balance was MUCH improved. On mine, the crank with the flywheel was 15 grams out of balance and with the pressure plate bolted on was 38 grams out of balance.

Having it zero balanced with the pressure plate on made a VERY noticeable improvement, not only does it accelerate smoother but faster as well since it isn't fighting itself.

I had other people tell me before that it had a strange vibration feel to it but I never really noticed it. I just thought that was how 383s felt. Now I know.

Good luck with the new build.

Interesting & noted for future reference.

Hope this engine runs great for you, Daniel. I love my 383.

Getting closer
 

Slowly but surely...

Daniel

Now that's a sexy post!!