On a 300hp 360 crate motor the 340 manifolds only made about 5 more hp than the 273 manifolds so I think you will not notice the differance. You could sell the 340 manifolds and get almost enough money for TTIs that made like 25 hp more than the 340 manifolds.

One of my favorite cheap upgrades is a JY thermo-quad in place of a 2bbl, or even in place of a small 4bbl.

Thin head gaskets are a good one. MOost replacements are .040 - .060 thick and investing in steel shim gaskets for a BB or the now discontinued mpoar .028 gaskets for a SB can bump compression a nice bit.

For small blocks I love the change from putting magnums on in place of any other factory head.

High ratio rockers always work good for me on mild cam motors. You can get them for a couple hundred bucks and a pair of valve cover gaskets are all thats required to put them on.

A mopar, or similar electronic ign up grade or even a piece it together your self electronic, works great over points.

For the 904 guys the low gear sets from the mid 80s and later low gear ratios work great, especially on a milder motor.