I'd give a set of L30 305 heads a try, they have a 58cc chamber IIRC.

L31 is rated at 255hp@4600rpm/330lb/ft torque@2800rpm
L30 is rated at 230hp@4600rpm/285lb/ft torque@2800rpm

Both engines use the same 191º/196º 0.412"/0.428" 111º LSA roller cam
The L30 305 is hampered with the single cat exhaust, while the L31 350 gets the better dual cat exhaust
Both engines use the same air intake, MAF, t-body, intake, injectors, manifolds, fuel pump FPR etc.

The L30 is only 25hp/45lb/ft torque down on the larger by 45cid 350.

the L30 heads can be had for much less than the 350 heads as well, look for numbers '520 and 059 for the 305 L30 heads.

But yes, you require the Vortec intake manifold.

peace
Hog