just digging this one up chaps, am i right in thinking that 21 and 28 engines of the same spec (std, se,sp) are essentially the same engine?

If there are any differences between them could someone let me know what. I assume its just port design and cylinder head alterations etc? I'm not yet sure of the exact spec of the 28 engine fitted to my 21, but i'm almost certain its topend rebild time and will be expecting re plating.

Are new barrels still available from honda?

One last question, the 21 loom i have has had both splices carried out GPS set to 3rd gear, would putting the 21 flywheel onto the 28 engine over advance the timing for the 28 transfer timing. Hoping perhaps of of the racers has caried out the same mod and can offer advice.

Cheers
Brendan