Htown,
I have gone back & forth with 2 MB's switching the engines from front rack to rear rack & putting on some miles both ways to determine which method of drive works best. I have never installed a bike engine in-frame so I can't compare to in-frame.
I prefer front drive...
Many people ask me what its like to have the weight of the engine out front & the best analogy I can come up with is if you were ever a newspaper boy & hooked up a plastic milk crate to your bmx handlebars with hoseclamps & loaded it up with your route full of papers.
Just make sure to keep the extra weight closer to the headtube & as low as possible.
I think it balances out the weight distribution on the bike better since your body is the heaviest thing on the bike & your butt on the saddle is more towards the rear of the machine.
Adding a rear rack & engine makes the front end squirrelly. Even with low bars as I have done by flipping a set of 5" riser bars upside down and getting body weight out front & lower. It helps but still not ideal.
Part of the fun of building these MB's for me other than riding them has always been trying to figure out new ways of making things go, using new ideas & implementing those ideas into a new build.
Many nights I wake up brainstorming a new way to attach this, or solve that...
I'd say, gotta give it a try (front wheel drive) for yourself to see if you like it. You can always take it apart & re-build as I have done too many times...lol
-lowracer-