I just had a thought. Remove the exhaust rocker and pushrod to get them out of the way. Use feeler gauges between the shaft hold down and intake rocker arm, on the intake port side. Keep adding feeler gauges until the pushrod goes in and you have ample clearance. My guess is the .350" you already have built in plus whatever the feeler gauge reads should be the correct amount of offset. Does not cost anything to try, and should show if a reasonable offset will work.
