Um...I need some advice.

Welcome to the forum. You should take the time to introduce yourself to the forum before you post any issues. Your topic is vague - next time be more specific. It will get peoples attention. Now that is out of the way.

In my opinion, I wouldn't use the Thruster fixie. Tires are too narrow for cruising at 30 mph.

The other 2 bikes may work, but your going to have to do your research on what others have done. Genesis Onyx looks like a recent discussion and the cruiser looks do-able at first look. Measure your engine and then measure the frame opening to see if the engine will fit.

Before you start building, look around the forum and see what others have done. Most importantly, take your time, be patient and listen to others advice.

Those engines are not just slap them on and ride, especially don't ride it all out or your going to shorten the life quickly. Your going to have to setup the engine properly and make some adjustments to get them dependable. Make sure you have tools or access to tools, especially a torque wrench and know how to use it.

Here's a couple guides to help you setup your engine and a couple more when you have problems. Every problem your going to have has already happened - it is just a search away to find the solution. Search before you ask.

https://docs.google.com/document/d/1GcesQihc7-mm3hJGf7UPiqOaRXZ8ekUT99QUZq2qXXE/edit

https://docs.google.com/document/d/1aBeJuoS--VQWwXysc07rpscTUbPzgc93xjiQBgsyFjc/edit

http://www.grubeeinc.com/USA/2 cycle engine trouble shooting guide.html

Good Luck,

Chris
AKA: BigBlue

Welcome ura.
BigBlue said everything.
Personally, I like the Onyx as a beefy looking cruiser type bike. Assuming it's appropriate.
I'll be following your build, post pics if you can- good luck!

I just built a Onyx with a 4 stroke motor in it. I call it the Black OX. I love this bike. I have also built two Schwinn late model China built cruisers and a Huffy Cranbrook. I sold the Schwinns and just yesterday sold the Huffberry. In my opinion the Schwinn is the easiest build and the Onyx is the best looking the Huff is just the Huff. For a first build I would go with a Schwinn. BTW I don't know how big you are but it seems like the China cruisers are all too short, bar to seat. The older Schwinns or the OX fit way better.

Oh man, don't accept mistreatment from the guy you send your hard earned fednotes! Use the search bar up top to check this out, there are dependable sources for these kits. I believe 2Door has recommended his source, and there are many others.
It's the power of our community. This place is awsome.

HAHAHAhaah Ura eight Tee Hee! Love it. Welcome to the fourm.

I'd go for your second or third choice too, nice looking bikes to start with.

Velodrome: I must be missing something... XIII is 13...

The ONEX makes a great bike but you have to be able to fab or buy big tube mounts and the gas tank is also an issue to mount. It is also aluminum so the chain tensioner requires more effort to secure. The Schwinn sounds like the best bet for your needs.
I've built all the bikes you mention and the Schwinn is overall the easiest and cheapest to build.
The fixie is not a good platform for a motor in my opinion. Too skinny and cheaply made.

I have actually built all three bikes. The schwinn del mar is going to be your best bet! Good solid bike.

Looking forward to your build thread...

Whatever you get look closely at all the weld points on the frame and look for the larger diamenter spokes on the wheels. Walmart cruiser bikes have both 12 gauge and 14 gauge spokes. avoid the cruisers with the smaller spokes. I've seen both types and even seen bigger spoked wheels on a less expensive bike. Read all you can here and Good Luck To Ya!