one thing to consider is what type of track ? tacky or dry slick ? if tacky then you want cubic inch with some stroke, if dry slick then short stroke to help make forward bite easier, a small bore from a 318 is going to limit the cylinder head, for a hobby stock class then a 318 may be built to run with 355s ci but for a faster class a 340 or 360 would be a better choice along with a w 2 head or a ported X head, i ran a 340 in a late model shaw car with flat solid tappet 2 barrel methanol stock rod X head 12.1 comp. it would run equal to any chevy 355-360 in its class but as you know chassi set up means more than horse power so good to have both, i was building a 340 w2 arias piston 13.1 with mechert hollow dome lite rods to run in a outlaw imca class but didnt get a car to put it in, also clearances were loose and a moroso wet sump pan was what i used with a direct drive powerglide 7500rpm max. i used a narrow rear main bearing in the block, i got most of my engine info from a guy who ran kit cars in the 70s and did well.