For all those people who want to play RSS with stock parts, a while ago I built a ModuleManager config that tweaks all stock engines to be in line with a somewhat arbitrarily chosen real world counterpart, tanks to realistic-ish mass ratio and pod/heat shields to afford a usable ballistic coefficient.
All crew modules have been tweaked too based on ISS parts
It probably needs some minor work for 1.2, but it is generated by a spreadsheet so it should take mere minutes.
Keep in mind that some things change drastically, such as some prices, some heat generation parameter (mostly based on energy density/mass) and monoprop engines being much weaker like IRL.
I was planning to publish it on CKAN back then, but then SMURFF came out and there's a significant functional overlap now.
Here's the mod https://github.com/z0rb1n0/LazyRSS
EDIT: accidental quote