just my $.02
if you have some extra time, and $$$
find a nice GTI of GLI A2, body with trashed engine
Find a wrecked '96-99.5 TDI complete (~$2500) and do a transplant
or get a good used, one-owner, A3 Jetta TDI or B4 Passat TDI, They are both quite superb, economical, quiet and fast (enough) ($3500-$8000)
only so much can be done to your IDI, boring is expensive on TD's when u need to buy pistons. So if you like to wrench, and experiment, you can play with the IDI's for awhile. But you may have $1000+ in parts + head work. The TDI long block is of limited value ?? You will need a pump, ECU and turbo... $$$ It is usually cheaper to buy a whole wrecked car than to piece stuff together.
Save you car $$ for what you want, (keep to a minimum), and buy 'distressed' real estate, or something that will make you 'passive income' I wish I would have done that 30 years ago...then I could wrench to my heart's content today, and not have to go to work everyday
, there is not enough time for fun + work + family