Not sure how I missed this one.
So you want to drop the bike 4". Here is what you can plan on.
Front suspension travel: 5.6" stock, 1.6" modified
Rear suspension travel: 3.6" stock, -0.4" modified
Ground clearance: 5.9" stock, 1.9" modified
You can forget trying to use any type of telescoping front suspension. The limited travel will bottom out on everything. Your only option will be to use a springer, or girder front end to get any reasonable travel. You will also need to come up with wheels, and a brake system that works with the front end.
The rear will already be past travel limit. Plan on doing a full hardtail treatment, and figuring out how to take care of the chain grinding on the sprocket cover.
With the limited ground clearance. You can send me that 4-1 as you will not be able to use it. A full custom exhaust is the only way you will be able to go. You can also plan on having the frame, and bottom of the engine drag on every speed bump, and driveway curb that you come across. That aluminum oil pan hanging below the frame will grind away quickly.
If you thought that you were going to do this on a budget. You can plan on $5K+ just to do what you need to drop the bike 4". By the time you get that far into it. You might as well spend the other $10-15K and go the full custom route. I am already $3k into a $300 project bike, and I have not even started on the frame yet.
Do not get me wrong. I am not saying that it can't be done. I am saying that it will not be cheap, or easy. Study every build up that you can read to find out what worked, and why something didn't work. Learn to ride while you are developing a plan on how to build the bike in your head.