Running Bantam Engine

Hi Guys
I wonder if any one out there has a bog standard Bantam (Running) engine, size unimportant, that I could loan, buy, swap?
I am working on my rolling chasse and I have to set up my riding position, and get used to riding a small bike I don’t want to get to the bikes first outing only to find out that I cannot change gear.
I went out on rex’s 175 and nearly dropped it on the first island (for some reason it didn’t feel like a 750 ZX7 R
my last bike).
I know I won’t be going fast so I’ll not know what it feels like at speed, but at least I will have an idea of the feel.
I have lot of places I can ride as long as I do not make a noise.
I hope some one may be able to help.
Thank you for taking the time to read this.
Colin