I have a heavilly modified 261 using Jahns 10:1 pop up pistons and they fit the stock, except for porting, cylinder head easily, so your Venolia's should fit too. Because mine is more race then street, I'm using an older,not in production, Clifford mechanical cam from 1970! It has held up well. Patrick's could be an ERSON cam or DELTA cam, both very good. You might want to search there sites. Can't help with other questions as I'm using home made intake exhaust, but, Fenton's are good. I would stick with the new style Patricks sells unless you are looking for something more period correct.Then I would seach for the cast style.They are readily available.

Drew