1300SP engine

My (new to me) '67 beetle has its original F numbered 1300SP engine which has never been apart to my knowledge. (one owner/family car). Still runs OK, but is getting a bit tired, I'll have to re-build her at some stage.

I'm not even sure if 1300 B&Ps are still available. My understanding is that the 1300 case is the same as 1500 and 1600 single-relief cases, so most people just put in 1600 barrels etc.

Are there any downsides to this? Are the heads the same as 1600SP? I had an idea that the head studs were a smaller size on the 1300 case. I've only really dabbled with 36HP and 40HPs, so not clear on the differences between later engines.

I only use it to potter around town, the 1300 is fine but I'm not sure how available the parts are.
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Thanks, Angus
Any tips would be helpful

not sure about the barrels but I thought that maybe the normal 77mm barrels could be used, to change over to 15/1600 would just require a barrel swap but your heads would need a bit of machining to fit the 1600 barrels