Cobba, with #1 piston at TDC, both #1 valves should be closed, with the correct tappet clearance and #4 exhaust valve almost closed and #4 inlet just about to open, ie "rocking. You can't improve on that for cam timing on s a David Brown or the majority of 4 cylinder engines, having a firing order of 1.4.3.2.
Personally, I doubt that your rough running is cam timing related. BUT I could be wrong. Been known to happen.
Steve.