Any 216,235 or 261 (or GMC) motor will bolt up to all 6 cyl. bellhousings from 1937 to 1962. The transmissions however are the snag. Sounds like you can get a manual tranny with the 235 deal, if that's the case your '48 passenger car bellhousing will not bolt up to this tranny. Bellhousings from say a 51 pickup will bolt to either your 216 or 235 and have the holes (one above another facing foreward) that your factory passenger 48 side motor mounts need. As you can see all the swapping can get complicated plus when you change something like a bellhousing then this affects the trans and crossmember and rear end etc etc. You can lean towards the stock bellhousing/trans/rear end to keep things simple or go all the way, it's up to you.
