Notice the push rod holes have been welded up ready to be re machined on big twin angles to make a Hybrid THUNDER-VO engine and have a PRO-SEAT conversion so they can be machined to accept 2" intake and 1.7" exhaust valves
Thunderstorm heads on the Big Twins
Performance engines need to breathe the stock 40mm CV is flow limited on a good set of heads to 100HP at the back wheel. Performance carbs will get you over that.
883 PRO-SEAT heads on the Big Twin SPORT-VO engine