Wood bed thickness question

[cgster]

My 67 fleetside truck I recently bought came with the bedsides but no wood was left in the bed. I've never dealt with replacing a wood bed before. I don't plan on going with oak wood at the moment and have been looking at other wood options but my question is, is 3/4 inch a required thickness for the wood to fit the bed correctly, or is that just the original wood thickness but not required? Thanks.