|>>|| No. 23045
>is putting an SSD in an otherwise fairly standard PC akin to trying to fit a turbocharged V12 into a shitbox Saxo (i.e a stupid idea that will result in everything blowing up)?
No. The rest of the system may represent a bottleneck but unless the system is genuinely ancient you'll still get an appreciable performance boost from adding it in. It won't "blow up".
Is there some reason you wouldn't put the SSD in the laptop and save yourself the cost of the desktop?
>after just running an in-built diagnostic test on it everything came up fine except the HDD which just said FAIL and nothing more.
That's likely SMART flagging up a predicted future failure. This failure, it should be pointed out, is not guaranteed.