Hi Tommy,
You asked me to report back on the Frateschi chassis when I got one, it finally arrived in the post during the week. It's a G12 chassis which I thought was the same as the G8 (and it may or may not be) having failed to get any definite answer from Frateschi in Brazil or the US distributor, so pretty much 'zero' for customer service.
That said, it's definitely too long for the inside of the MIR kit and in all probability the bogies will foul in the inside of the chassis especially on curves. Haven't had time to get to it but will likely need a will a cut and shut to remedy this. So much for it being HO! Fortunately I did not invest a huge sum in it as it was purchased used in NZ livery on eBay, still significantly cheaper than acquiring on in the US or from Brazil (due to the postage cost)
The bogies look prototypical versus the Athearn SW1500 chassis which Gerry is using but I'd bet the Athearn's running characteristics are better. The Frateschi is noisier then my lone Atlas switcher and way noisier than a MM 141. Max speed like the 141 is not that fast, slow speed is not that slow but it pulls very well. The catch is that he weights are mounted fore and aft snugly inside the BODY. It's likely they might not fit easily somewhere on the chassis under the MIR body without running a drive shaft through the weights, in which case there should be plenty of room between the flywheels and gear towers.