I just have an observation. In your opening post you say the bike is a 77, then you say "Stock spec is fine for my stock displacement 750."
The only stock 750's built on the XS650 platform were not 77's, they built 200 in 72 so the could race a 750 engine.
Now back to your question. To replace the Boyer with a Pamco, remove all Boyer parts.
Being a 77 it had points as stock. If your still using the stock cam it should still have the bushings in the cam.
blackbetty mentioned that you need the atu and parts as the points needed.
That depends on which Pamco you get. The original does need the ATU, the new E-advancer Pamco doesn't need the ATU. It does need the advance rod and the pins that go in the rod and the pin that goes in the cam that held the ATU too the cam.
As far as being high performance vs stock, stock was weak and barely ran the engine. The only thing that makes it high performance is the coil.
On the coil a stock 80 TCI coil will run fine. They have around 15vk output. This will run the bike just fine. A coil with a higher output will run better. This higher voltage allows the use of higher performance plugs as well as being able to open the plug gaps a bit.
These things make for a larger hotter spark.
A big hot spark starts easier runs better.
On Pamcopete's ignition web site he has a chart showing this. He list several coil and plug combo's and the fuel mileage of the combo's. This increase in mileage indicates an increase of the engine's effienecy. This increase was just a change of coil and plugs. This also indicates more horsepower for the amount of fuel consumed. A bit more power lets you use a bit less throttle to do the same job.
On the Pamco you can use any dual output coil that has a 2.5 to 4.5 ohm primary ohms. Many bikes and even cars use coils of this type. Harley has forever. The coil can have most any brand name Harley, Accel, Dyna, and many other brands.
If you do a search on this forum you will find references to many coils, how to mount and wire. Once you find a coil that sounds like it sparks your fancy then shop around for the best deal.
And that may be with one of the kits from Mike's. They have both the original and e-advancer Pamco's in kits from just the ignition up to everything you can use.
On your 77 if you still have the advance rod and pins the kit #14-0910 has the rest of what you need. If you don't have the rod then kit #14-0913 has the rod. These are e-advancer kits.
For the original then kit # 14-0901 is what you need if you have the stock ATU and rod. Kit #14-0902 has the ATU and rod.
The #14-0905 and 07 are the e-advancer with a lesser coil.
There are other options on the ignitions that you can mix and match so you can use part of what you have or a coil from some other place.
Shop around and see what you like.
Leo