Would you have to notch the block for the larger 318 Valves?
I build my 273 with a stock oil pan and MP windage tray-I like it.
I would choose the aluminum intake for the weight issue.
To put hydraulic lifters in a 273 requires different pushrods than 273 stock.
The 340 grind is significantly different from 273 stock and may require some problem solving.
The stock install for my aftermarket Lunati cam is 4 degrees advanced-I degreed it in to that.