AFV Club 155mm Long Tom (& M4 HST)

Updated my Journal today; some good news but I had hoped to have gotten further & had pictures at least of the M5 Limber, but ...

Anyway, need suggestions for two things:
-- kit has a metal gun tube (well half of it) that has no rifling at the end (unlike the later 8" kit) -- any ideas how I might add same ???
-- kit has a nice breech block with thread detail, but the breech itself has no detail (ie, matching threads) -- any ideas ???

Thanks in advance ....

An update (here because under 24 hr Journal limit) on the PSP 35039 wheels & tires -- I got into them today. Quality is a bit uneven. The tread depth varies & not as per real wear, but it may not be a real problem. I found some tiny airholes vicinity of the sprue attachment. I also found some tires & a couple wheels to be lop-sided (or bent) -- almost looks like they modelled 'em after a junkyard. I think the whel parts will be OK when glued in, and I think I can hide the tires on inner bogies.