... but that's why it is called modeling and not assembling.
IIRC, the hiccup, if you can call it that, is the Merc interior shell does not have doglegs like the Galaxie, so there may be some interference with the aft part of the chassis. You may need to adjust the wheelbase slightly, requiring an insert of some kind to stretch the chassis fractionally and get the wheels in the right place for a good 'sit'. Come to think of it, maybe to the chassis fitting first - and when it is in place, go after any interior issues.
The Merc comes with some excellent pent-roof 'script' valve covers, a nice air filter and very good dual 4-bbl intake. The production numbers of '65-6 427 Mercs were tiny - even though it was listed as an option, total for each year was miniscule.