As I understand it, this pump of unknown origin has a cast iron body, whilst the SRM one has an aluminium body. Assuming - and this is the operative word - that the materials and machining are of equal quality, then the cast iron pump will be best.
Gear pumps are a pain generally, as they tend to lose pressure when hot. And an aluminium body magnifies the problem, due to expansion of the body away from the gears.
The original pumps in the singles were of a zinc type material. It would shrink on the spindles and wear around the gears. Changing to an aftermarket cast iron gear case was a huge improvement.
But at the sort of money being asked - SRM or 'hepolite' - I'd rather make my own. If the pump we're talking about was in volume production, manufacturing cost would be around £1 each. But this is limited batch production, so the price will obviously be higher. But 300x? If it can't be sold for £100 retail, someone needs to look at the production process, especially with the advantage of today's CNC machines.
It has been my policy for years, that if something's worth £1000 then I'll happily pay £1000 for it, but I refuse to pay £1000 for something that I know is only worth £20. Having been in research and development (hence my handle) I know it is not uncommon for a retail price to be 20x the value to the manufacturer. In the 70's when I was working on transmission design, I learnt a certain major motor manufacturer would only pay $15 for a car differential. The retail price at the local dealer was £650. A pressure release valve worth perhaps 2p retailed at £8. And Ford's 6 litre 6 cyl diesel engine owed them £50 - the retail price of the engine's gasket set. People generally don't realise how much they're paying over the odds.
