Did you ever find out? Going to make my own tool as well.

 

One of the 50s kid videos had a DIY spring compressor. Maybe there’s a link or directions there to make one?

 

There was a time when we were replacing valve springs, retainers and collars some 10 times a year, on M50 based (virtually the same) engines. Owing to spring and/or camshaft upgrades. I got tired of all the flimsy (on the car) tools.

I took a used camshaft tray, cut it on the bandsaw. and opened up the outsides just a little. Cleaned up the rough edges on a grinding wheel.

I place two large washers (with large hole in the center) over the two valves to be done. Insert compressed air into cylinder to hold the valves up. Stack a few nuts on top of the jig and use the nuts from the studs to crank it down evenly.

Fast, easy and no tools popping off and keepers/retainers flying off to who knows where.

 

A to A1 = 37mm ; B to B1 = 45mm

 

My hack tool, hope it works!

 

My hack tool... hope it works! View attachment 941439

As long as the lower plate doesn't flex? Good to go!