graybarkhunter,the weight washers aren't an option.You can only fit 3 on before running out of threads and strength isn't as good as a solid head,screwed tightly against the insert.
I think your best option would be to buy the VPA glue on SGT,150 gr with a 75 gr steel adapter or their 125 gr SGT,with a 100 gr adapter.The VPA Small Game Thumper is an excellent,high quality head and by combining a glue on head with the appropriate weight insert,you can make almost any weight you want.Just clean the parts and glue with a good epoxy.It is a very simple and non-critical project.