Could anyone give me some guidance
That's a good question.
From experience, it's a lot of trial and error. And it was a lot of time measure and cardboard engineering before anything went down to the engineering firm.
A Vernier caliper is going to be helpful. A decent tape measure and a long straight edge.
The first thing I did.
With the brakes and spacers removed. The Front and rear wheels on the bike and the bike on the ground.
I used thick 3mm washers to align the front wheel to the rear wheel. You will want to get those perfectly inline and measure the offsets.
Once you know this, you know how much machining you need to do to the wheel spacers to get those inline.
The next thing you need to figure out is how to get the front and rear sprockets inline.
Once you know how much padding or machining the rear wheel needs, you can determine the rear spacer size.
From here you then need to sort the brakes out.
Starting with the rear, merely place the caliper over the disc, and measure the offsets to the carrier. Machine the carrier or brackets to suit.
Repeat for the front, place it on and create a cardboard cut out of the carrier necessary.
Ensuring strength in the brakes design must be key. A curve following the disc is probably best advised. I had mine made out of Ally, but steel would be preferred.
@ricky0115 No, because I presume the tyre widths are going to change.
The Tyre might be offset due to the carrier position moving.
Should have explained, that's what the straight edge and tape measure and verniers are.
So you need to run it across the length of the bike measure the distance between the two sides of the front wheels
You won't want to rush this. It's a timely procedure that determines the rest of the build. Get it wrong and all your measurements for future fabrications will need changing.
If you don't get the wheel alignment right, it'll just start crabbing down the road.
@ricky0115 Nah, you need to scrap everything you know about the rear wheel and start fresh.
The sprocket size will alter the speed, but that's way way ahead of where you are today.
Ultimately I had my sprockets custom made by renthal, so sprocket sizes are not the issue.
The issue is getting the fitment right.