They will be fine... Throw some 2.02 intakes in them and let them flow...
The J heads took over for the x heads mid year 1970, 340's had j heads with 2.02 intakes from mid 1970 model year through 1971 model year, they will be fine with 2.02 intakes...
In 1971, the j heads came with 2.02 intakes for 340's and 1.88 intakes for 360's... They will work with either valve...
