Hi Guy, the concave Pistons would probably be the originally fitted 6.5:1 compression ratio Pistons but I've not seen any new ones of those for sale (not that I've really looked), so called flat top Pistons are around 7:1 and seem accepted to be good compromise between power and torque, domed Pistons would probably be 8:1 or more and would change the engine characteristics quite a lot compared to concave.
I'm not sure what the freight and import duty would be in Kenya but In the past I've shipped new Pistons from uk to New Zealand using Draganfly and also British only Austria and it was not too expensive as I guess they do not weigh that much. Oddly I bought Australian made Pistons from Draganfly in the uk, as it was cheaper than than buying the same Pistons from our cousins in Aussie!
If the skirts are damaged I'd would aim to keep max sleeve thickness and strength? Depending on the damage (pics would help here, we love pics
).
I've got flat tops in my GF and a 356 (super rocket or late golden flash) cam and the engine is still docile and torquey at low revs, but then again I kicked over an A10 recently that had never had the engine rebuilt and it was really easy to kick over compared to mine
maybe it was low on compression due to wear though.........