I think that the lifters work for all buick v8's and the 3.8 v6 There is a difference between the pre '70 and '70 and up engines, however. If your 350 is a '68 or '69, then your lifters will work on his 300.
I'd recommend the advise in the above read with the 9 slot timing gear. I only had 3 and had a heck of a time degreeing. Jumping teeth to find out i need to use a diffrent keyway slot. took a long time to figure it out. oh and to use the right numbers on the cam wheel.