Clean out soft-top drain

[enuff_zed]

Keen to keep the car original if possible and not relocate the roof

That's an admirable intention. However, if the drains have been blocked already then there is a better than even chance that the plastic tub the motor sits in is already full of water. Even if that has drained away the insulation will be soaked. So your motor will still be sitting in a wet environment and getting more corroded by the day until eventually it'll cry enough.
You have a few options really:
Leave it where it is and keep your fingers crossed.
Relocate it to the boot before it dies
Take it out, check it and put it back with clean dry insulation, and some drain holes drilled in the bottom of the casing.

There is likely to be water still sneaking into the motor tub even if the drains are clear.

[dva99999]

This is my first post (except the newbie bit) and one of the problems I had was lack of space in my garage on the passenger side. I found that it is possible to remove the splash guard and plastic bracket without jacking the car up. What this also meant that when I ran water through it, it went straight through the drain hole and not along and out the seams like the drivers side.
I used coat hanger wire and welding rods to really loosen it. Next week is when I’ll tackle the job of relocating the motor but for the time being I’m pleased. It was only clean water that came pouring out initially. The previous owner had washed it before I picked it up.
Thank you