Rero fit roller cam & lifters into early block?

These are the same lifters I have in my 340. They are a drop in lifter, just know that you will have to open up the Pushrod holes so you can get the correct angle for the lifters. I also recommend that you either get a set of adjustable 273 rocker or a set of roller rockers (I have a set of comp pro mag roller rocker on the motor).
You'll need to be using a roller cam, just make sure that roller cam has a cast iron intergrated gear on it, otherwise you'll be using a broze year and will be ripping the motor back apart in about 3000 miles. I got my cam from crane because it has a cast iron gear on it and I run a hardened intermiate shaft.