You can improve efficiency with a cam upgrade and a higher compression piston, and you can still use the stock carb if you wish to save $$.

The Stage 3 is $299 with a refundable core exchange deposit of $100, so $399 total and $100 back upon my receipt of your usable cam core.
The 94mm Wiseco is $199.

Opening the exhaust port a bit is easy to do with a drill and a metal rasp bit and some sanding cones.  You don't necessarily need to go deep inside, just open the outer ring and smooth down the top of the ridge a little behind the outer ring.

If you want a larger header and a good flowing muffler, a proper dyna works very well for the engine, and you can have a header made at a muffler shop for less than ... mine was done 8 years ago I think ...for: less than $20 for 8' of pipe and used 4', and $40 labor for cutting and welding, and that was in the Columbia SC area.  A custom unit will cost $250 for stainless and you've got to send them a pipe to duplicate.

Anyway...
You can improve your engine for not a lot of $$, and it can be done a piece at a time if needed.

This is interesting stuff.

I would think if drilling the oil holes in the cam reduces oil pressure it would make sense to increase the center hole size to insure oil flow to the end of the cam.

On the engine I am working on that was run without oil the two main cam bearing surfaces were only slightly damaged while the steady bearing was completely destroyed and that end of the cam had a groove worn into it. When inspecting it I found it very strange. There was a small amount of oil still in the engine. My guess is the steady bearing had less oil...