Not my first but my most ambitious project was rebuilding the engine on a ‘59 Austin Healy Sprite. Took the block to a machine shop for overbore and had head milled; reassembled with new bearings, pistons, rings, etc... When finished, installed in car, connected fuel, electrical and started. No oil pressure....zero.
Shut off.... After thinking about the problem, went back to solvent tank and recovered the small pressure-relief valve and installed it in the side of the engine. YES! Oil pressure good and it ran great. Drove it two years and sold it for $75 more than I paid for it.
Those are neat cars. I have known more than a few British car fans who have cut their teeth on an Austin Healy Sprite.