The Mopar race blocks are super heavy, my 340 resto block weighs 211 lbs bare. That is about 60 lbs more than a factory 340 block.

Good luck getting a set of roller lifters to fit in a 340 resto block. You'll need to do a lot of grinding and machine work in the valley and you still might not get it to work. Just be prepared for a lot of mocking up and re-work. I spent a lot of time machining and grinding in the valley of my block for hyd roller lifters and finally gave up. I'm now trying to see if solid roller lifters will fit. I've tried a couple of sets so far and they don't work so we'll see what happens. I have a new set from Comp on the way that they say will work.

The Magnum race block from Mopar might work but I haven't tried one. They have the valley machined for hyd roller lifters which probably means that solid roller lifters will clear but Mopar doesn't publish any pictures or provide any detailed info on the block so you basically have to do the R&D yourself.