Struggles after 4900 rpm

Now that you have bumped up the initial to 19btdc you might be running more than the max 34-35 degrees with full mechanical advance, if you can I would invest in a timing tape to make sure you are not exceeding the 34-35btdc at 2500rpm (mechanical advance all-in).

If you have the vacuum canister hooked up then you shouldn't exceed 50btdc at cruise speed (part throttle, high vacuum with timing all in). Too much advance might result in detonation and you can't always hear it.

Did you set your initial timing with a timing gun and with a vacuum gauge hooked up? The engine will let you know where it wants to be. Set the initial timing to where you get the highest vacuum rating (vacuum gauge hooked up to manifold port not the ported on the carb). Make sure while doing this you keep the idle rpm low so the distributor doesn't add in any mechanical advance. Once you figured out where the initial timing want to be then you'll have to limit the mechanical (centrifugal) advance to 34-35 degrees.

Have you checked the spark plugs for any sign of detonation?

Since you changed a few things before this happened you can always change individual items back to how they originally where just to check if any of the items are bad. Old spark plug wires can look good but miss or spark-over at high rpm. Just a thought.

Good luck.