When Intermountain first came out with their F7 shell, they did not have a chassis ready to sell with it at the same time. So modelers were using Stewart (now Bowser) chassis.
You should be able to get a Stewart or Bowser F unit chassis - there should be plenty for sale on Ebay and other outlets.
So basically the Intermountain F7 shell was manufactured to fit on the Stewart/Bowser/KATO chassis so that it could be used by modelers until Intermountain brought their own chassis to market a year or so after release of the shell. That way they could sell the shells and start making money while they tooled up and produced the whole enchilada. Intermountains own chassis would be dimensionally the same in the aspects important to mounting the shell.
Rio Grande. The Action Road - Focus 1977-1983
With a little work, the Proto1000 F3 chassis works with the Intermountain shell too. IIRC, the main things to watch are the rear coupler mount (may need to grind so that it fits inside the shell), and the tabs on the inside of the shell will need to be ground down slightly to avoid having the shell bulge outward.
Robert Beaty
The Laughing Hippie
-----------------------------------------------------------------
The CF-7...a waste of a perfectly good F-unit!
Then it comes to be that the soothing light at the
end of your tunnel, Was just a freight train coming
your way. -Metallica, No Leaf Clover
The Regal Drive/ chassis is what IM came out w/ after offering the shells. The Stewart/ Bowser will be the easiest drive to find though. The early Stewart/ Kato is actually the best drive if you can locate one. The later Boswer runs quite well, my issue is the truck wires are rather heavy and stiff. It should not be trouble as the chassis is quite heavy. These are usually found new for about $40- 60. The Kadee #450 close coupling conversion is the recommended coupler. It will fit the Kato or the Bowser. The "torsion" spring of the #30 series can be a pain for first time assy, but they actually are one of the best operating couplers for that engine.
Modeling B&O- Chessie Bob K. www.ssmrc.org
Yes, agree the original Stewart KATO chassis are hard to beat. I've still got 13 Stewart F units and love them - even though the shells are not quite up to Genesis standards, the drives are great. You can use standard Kadee #5 couplers in them if you cut the "ears" off the coupler boxes that come with them, but the Kadee #450 is the "close coupling" conversion that gives a scale 3 feet between the units. To save money, I only use the #450 on the back end of the F7A and both ends of the F7B units. The front of the F7A the #5 works fine and will clear the pilot.