The orange wheels are BRMs and are 16" and will fit some large brakes - larger than you need for a GT40.
The blue car is a "pure" MKI.
The white care is a MKI as well, but with MKII periscopes.
This is a MKI and MKII side by side.
And this page at ERA shows the differences.
ERA MK II Page
MKIIs were made to take the 427 FE motors which are much heavier and larger than the Windsors. With modern Windsors there is no need to use the FE motors - you can get more from a Windsor anyhow.
The RF kit does not accept a FE engine, but the ERA kit will which makes it more realistic from that standpoint. No AC though.
Duct work can be functional without difficultly and was used for oil coolers, tranny coolers, and brakes depending on the setup.
Ron
[ February 22, 2002: Message edited by: Ron Earp ]