I already told you what to do here:
V-8 Mount problem
Sounds like you are still trying to mix old style mounts with new style. Don't use the 283 rubber block mount!
Use a seventies 350/305 all steel "clamshell" engine mount and the rubber frame mount from a 305 or 350 4th gen Nova. The RUBBER frame mount you can buy new at the parts store. Say: " I need a pair of motor mounts for a 78 305 Nova, please".
Bolt these to the frame in the appropriate holes.
The clamshell mounts are common as dirt in the junkyard. 70's Caprices, Novas, Malibu's, Camaro's, Pickups...just about anything with a Chevy SBC except a Monza. Tell the junkyard you need a pair of 305 or 350 Chevy engine mount brackets that will fit your 4th gen Nova. Bolt these to the engine. Make sure you get the long cross bolts at the bone yard too.
If you are having this much trouble with standard engine mounts then your going to have trouble with engine brackets because the 283 heads don't have accessory holes. You'll have to use old style brackets and pullies with the short water pump. That means the fan won't fit the shroud. If you switch to a long water pump then the fan will fit but the pullies won't align.
I'm not sure it's worth the headaches to install a little 283. The fuel economy will be less than the six and the power will be less than than you think.