Your 1950 Chevrolet, if it came from the factory with a standard transmission, had a six-cylinder inline of 216 cid. The "300" cid engine that your uncle or someone installed must be positively identified before anyone can determine what flywheel to find and use. It could be a GMC (302 cid) or a bored-out Chevy 292, or something else. . . .
If the engine is a GMC, then you should find casting numbers on the driver's side of the block, just above the oil pan. You may have to clear away some grease to see them. You'll find lists of casting numbers for both blocks and heads on a link to the left of your screen. When you have matched the numbers, you'll know what engine you have. It will probably also be useful to determine what bell housing and transmission your uncle used.
As to whether you should undertake the conversion to twelve volts, that depends on your mechanical experience and aptitiude with automotive electrical systems. Finding someone with experience to work with you on it can help you get the job done and perhaps further your education.
God's Peace to you.
d
Inliner #1450
