Aye Ian,
Used to use the "silencers" from the end of the VW Beetle system, they effectively take the "crack" off the exhaust note, don't impede gas flow and are relatively cheap and easy to purchase. I understand why you initially wish to keep costs down, until you have the beastie up and running and see how you meld with it.
As for the cylinder base nuts!
They look a right pain in the buttocks. But, torquing, allen cap screws at the base of an SRX cylinder can be "trying" as well!
I'm still cleaning carbon and crud from the internals of the Ducati 350 at present, inbetween other household chores etc.
Good health, Bill